swift package --help doesn't show subcommands provided by plugins (#9284)

Modified swift package --help in order to include possible commands
provided by command plugins
### Motivation:

Fixes #9226

### Modifications:

Overrode --help and -h of swift package command to also include, after
printing the help message, the output of swift package plugin --list

Added tests to support change too

### Result:

After --help message is printed, users will see a new section (whenever
needed) called AVAILABLE PLUGIN COMMANDS:

`
completion-tool         Command to generate shell completions.
plugin Invoke a command plugin or perform other actions on command
plugins.

  See 'swift help package <subcommand>' for detailed help.

AVAILABLE PLUGIN COMMANDS:
benchmark (plugin ‘BenchmarkCommandPlugin’ in package ‘Benchmark’)
`

---------

Co-authored-by: John Bute <johnbute@Johns-MacBook-Pro-4.local>

Author: johnbute

Sources/Commands/PackageCommands/APIDiff.swift

@@ -26,7 +26,8 @@ import Workspace
 struct DeprecatedAPIDiff: ParsableCommand {
     static let configuration = CommandConfiguration(commandName: "experimental-api-diff",
                                                     abstract: "Deprecated - use `swift package diagnose-api-breaking-changes` instead",
-                                                    shouldDisplay: false)
+                                                    shouldDisplay: false,
+                                                    helpNames: [.short, .long, .customLong("help", withSingleDash: true)])
 
     @Argument(parsing: .captureForPassthrough)
     var args: [String] = []
@@ -49,7 +50,9 @@ struct APIDiff: AsyncSwiftCommand {
         behavior may be undesirable as the comparison can be slow. \
         The `--products` and `--targets` options may be used to restrict the scope of \
         the comparison.
-        """)
+        """,
+        helpNames: [.short, .long, .customLong("help", withSingleDash: true)]
+    )
 
     @OptionGroup(visibility: .hidden)
     var globalOptions: GlobalOptions

Sources/Commands/PackageCommands/AddDependency.swift

@@ -27,7 +27,8 @@ import class PackageModel.Manifest
 extension SwiftPackageCommand {
     struct AddDependency: SwiftCommand {
         package static let configuration = CommandConfiguration(
-            abstract: "Add a package dependency to the manifest."
+            abstract: "Add a package dependency to the manifest.",
+            helpNames: [.short, .long, .customLong("help", withSingleDash: true)]
         )
 
         @Argument(help: "The URL or directory of the package to add.")

Sources/Commands/PackageCommands/AddProduct.swift

@@ -35,7 +35,9 @@ extension SwiftPackageCommand {
         }
 
         package static let configuration = CommandConfiguration(
-            abstract: "Add a new product to the manifest.")
+            abstract: "Add a new product to the manifest.",
+            helpNames: [.short, .long, .customLong("help", withSingleDash: true)]
+        )
 
         @OptionGroup(visibility: .hidden)
         var globalOptions: GlobalOptions

Sources/Commands/PackageCommands/AddSetting.swift

@@ -35,7 +35,8 @@ extension SwiftPackageCommand {
         }
 
         package static let configuration = CommandConfiguration(
-            abstract: "Add a new setting to the manifest."
+            abstract: "Add a new setting to the manifest.",
+            helpNames: [.short, .long, .customLong("help", withSingleDash: true)]
         )
 
         @OptionGroup(visibility: .hidden)

Sources/Commands/PackageCommands/AddTarget.swift

@@ -42,7 +42,8 @@ extension SwiftPackageCommand {
         }
 
         package static let configuration = CommandConfiguration(
-            abstract: "Add a new target to the manifest."
+            abstract: "Add a new target to the manifest.",
+            helpNames: [.short, .long, .customLong("help", withSingleDash: true)]
         )
 
         @OptionGroup(visibility: .hidden)

Sources/Commands/PackageCommands/AddTargetDependency.swift

@@ -26,7 +26,9 @@ import Workspace
 extension SwiftPackageCommand {
     struct AddTargetDependency: SwiftCommand {
         package static let configuration = CommandConfiguration(
-            abstract: "Add a new target dependency to the manifest.")
+            abstract: "Add a new target dependency to the manifest.",
+            helpNames: [.short, .long, .customLong("help", withSingleDash: true)]
+        )
 
         @OptionGroup(visibility: .hidden)
         var globalOptions: GlobalOptions

Sources/Commands/PackageCommands/ArchiveSource.swift

@@ -21,7 +21,8 @@ extension SwiftPackageCommand {
     struct ArchiveSource: AsyncSwiftCommand {
         static let configuration = CommandConfiguration(
             commandName: "archive-source",
-            abstract: "Create a source archive for the package."
+            abstract: "Create a source archive for the package.",
+            helpNames: [.short, .long, .customLong("help", withSingleDash: true)]
         )
 
         @OptionGroup(visibility: .hidden)

Sources/Commands/PackageCommands/AuditBinaryArtifact.swift

@@ -24,7 +24,8 @@ import struct TSCBasic.StringError
 struct AuditBinaryArtifact: AsyncSwiftCommand {
     static let configuration = CommandConfiguration(
         commandName: "experimental-audit-binary-artifact",
-        abstract: "Audit a static library binary artifact for undefined symbols."
+        abstract: "Audit a static library binary artifact for undefined symbols.",
+        helpNames: [.short, .long, .customLong("help", withSingleDash: true)]
     )
 
     @OptionGroup(visibility: .hidden)

Sources/Commands/PackageCommands/CompletionCommand.swift

@@ -22,7 +22,8 @@ extension SwiftPackageCommand {
     struct CompletionCommand: AsyncSwiftCommand {
         static let configuration = CommandConfiguration(
             commandName: "completion-tool",
-            abstract: "Command to generate shell completions."
+            abstract: "Command to generate shell completions.",
+            helpNames: [.short, .long, .customLong("help", withSingleDash: true)]
         )
 
         enum Mode: String, CaseIterable, ExpressibleByArgument {
@@ -93,4 +94,4 @@ extension SwiftPackageCommand {
             }
         }
     }
-}
+}

Sources/Commands/PackageCommands/ComputeChecksum.swift

@@ -19,7 +19,9 @@ import struct TSCBasic.SHA256
 
 struct ComputeChecksum: SwiftCommand {
     static let configuration = CommandConfiguration(
-        abstract: "Compute the checksum for a binary artifact.")
+        abstract: "Compute the checksum for a binary artifact.",
+        helpNames: [.short, .long, .customLong("help", withSingleDash: true)]
+    )
 
     @OptionGroup(visibility: .hidden)
     var globalOptions: GlobalOptions