Enhance language tag functionality with normalization, validation, and equality checks

[ptr727]

• Added normalization methods for ExtensionTag and PrivateUseTag to ensure consistent casing and ordering of tags.
• Implemented equality checks and hash code generation for ExtensionTag and PrivateUseTag.
• Updated LanguageTagBuilder to throw an exception for empty extension tags.
• Enhanced validation in LanguageTagParser to reject whitespace in extension tags.
• Added tests to verify new behaviors and ensure robustness.

[Copilot]

Pull request overview

This PR enhances the language tag functionality by adding proper equality semantics, normalization capabilities, and improved validation for extension and private use tags. The changes also include a bug fix for exception handling in the HTTP client resilience policies and removal of unused code.

Changes:

• Added case-insensitive equality comparison and hash code generation for ExtensionTag and PrivateUseTag records
• Enhanced validation to reject whitespace in extension tags and empty extension collections
• Fixed HTTP client resilience handler to properly handle exceptions in addition to unsuccessful status codes
• Removed unused helper methods from Program.cs

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
LanguageTags/LanguageTag.cs	Implemented Equals() and GetHashCode() methods for ExtensionTag and PrivateUseTag to support case-insensitive, element-wise comparison
LanguageTags/LanguageTagParser.cs	Enhanced ValidateExtension() to check for whitespace characters and added empty extension validation
LanguageTags/LanguageTagBuilder.cs	Added validation to throw ArgumentException when attempting to add empty extension tag collections
LanguageTagsTests/LanguageTagTests.cs	Updated tests to verify case-insensitive equality and removed unused System.Linq import
LanguageTagsTests/LanguageTagParserTests.cs	Added test case for extension tag with whitespace validation
LanguageTagsTests/LanguageTagBuilderTests.cs	Added tests for empty extension validation and whitespace rejection
LanguageTagsCreate/HttpClientFactory.cs	Fixed resilience handler to check for exceptions in addition to unsuccessful HTTP status codes
LanguageTagsCreate/Program.cs	Removed unused GetCommandLineOptions() and GetCancellationToken() methods