Standardize file paths when attempting to find toolchains

`containingXCToolchain` loops infinitely when given eg. `C:\foo\..\bar`.
The underlying cause is that `deletingLastPathComponent` does not remove
the `..` on Windows. On macOS it's potentially worse - it *adds* `..`.
We don't see the infinite loop on macOS/Linux though because
`AbsolutePath` already removes them (which is not the case on Windows).

Resolves #2174.

Author: bnbarham

Sources/ToolchainRegistry/Toolchain.swift

@@ -369,7 +369,7 @@ public final class Toolchain: Sendable {
 func containingXCToolchain(
   _ path: URL
 ) -> (XCToolchainPlist, URL)? {
-  var path = path
+  var path = path.standardizedFileURL
   while !((try? path.isRoot) ?? true) {
     if path.pathExtension == "xctoolchain" {
       if let infoPlist = orLog("Loading information from xctoolchain", { try XCToolchainPlist(fromDirectory: path) }) {

Tests/ToolchainRegistryTests/ToolchainRegistryTests.swift

@@ -336,7 +336,7 @@ final class ToolchainRegistryTests: XCTestCase {
 
       try ProcessEnv.setVar(
         "SOURCEKIT_PATH_FOR_TEST",
-        value: ["/bogus", binPath.filePath, "/bogus2"].joined(separator: separator)
+        value: ["/bogus/../parent", "/bogus", binPath.filePath, "/bogus2"].joined(separator: separator)
       )
       defer { try! ProcessEnv.setVar("SOURCEKIT_PATH_FOR_TEST", value: "") }