[WIP] Make reflection cache classes public and add XML documentation

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

Please make the following changes to the reflection cache infrastructure on top of the existing branch copilot/add-reflection-cache-settings:

Changes Required:

1. Make Classes Public

Change the following from internal to public:

• ReflectionCache class
• PropertyWithAttribute struct

2. Add Comprehensive XML Documentation

Add complete XML documentation to all public types and members including:

For ReflectionCache class:

• <summary> describing the class purpose
• <remarks> explaining:
  • Thread-safety (uses ConcurrentDictionary)
  • When to use (opt-in via ReflectionCacheSettings)
  • Performance characteristics
  • Cache is unbounded but finite (only request types)
• <example> showing usage:

  // Enable caching at application startup
  ReflectionCacheSettings.EnableReflectionCache = true;
  
  // The cache is used automatically by ParameterUtils

For GetRequestParameterProperties method:

describing what it returns with full description describing the return value explaining caching behavior (only caches when enabled) if type is null For PropertyWithAttribute struct:

describing the struct purpose explaining it pairs PropertyInfo with RequestParameterAttribute For Property property:

and tags For Attribute property:

and tags For constructor:

describing construction tags for both parameters For ReflectionCacheSettings class: Enhance existing documentation with: More detailed about thread-safety considerations When to set it (before any API calls) Impact on both Google.Apis.Core and Google.Apis assemblies Memory and performance trade-offs 3. Update Tests Update test documentation to reflect that these are now public APIs.

Important Notes:
These classes are in the Google.Apis.Util namespace
They're located in Src/Support/Google.Apis.Core/Util/
Follow Microsoft's XML documentation standards
Include cross-references using where appropriate
Explain the opt-in behavior clearly in remarks
Context:
This addresses the maintainer's concern about InternalsVisibleTo causing version coupling. Making the cache public allows both Google.Apis.Core and Google.Apis assemblies to share a single cache instance, avoiding memory duplication while preventing tight version dependencies.

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