Add polyfill for string.GetHashCode(StringComparison)

[Tyrrrz]

No description provided.

[Copilot]

Pull request overview

This PR adds a polyfill for the string.GetHashCode(StringComparison) method that was introduced in .NET Core 2.0. The implementation delegates to the appropriate StringComparer based on the provided StringComparison enum value, enabling backward compatibility for older framework versions.

Key changes:

• Implemented GetHashCode(StringComparison) extension method using a switch expression to delegate to corresponding StringComparer instances
• Added basic unit tests to verify hash code equality for identical strings and case-insensitive comparisons
• Updated documentation to reflect the new member count (171 members, 233 total signatures)

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
PolyShim/Signatures.md	Updated member and total signature counts to reflect the addition of one new string method
PolyShim/NetCore20/String.cs	Implemented the GetHashCode(StringComparison) polyfill using switch expression with conditional compilation for InvariantCulture cases
PolyShim.Tests/NetCore20/StringTests.cs	Added basic test coverage for Ordinal and OrdinalIgnoreCase comparisons

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (8d07b6d) to head (07072f3).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@     Coverage Diff      @@
##   master   #53   +/-   ##
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