Add polyfill for File.AppendAllBytes(...)

[Tyrrrz]

No description provided.

[Copilot]

Pull request overview

This PR adds a polyfill implementation for the File.AppendAllBytes(string, byte[]) method introduced in .NET 9.0, enabling its use in earlier .NET versions.

Key changes:

• Added synchronous AppendAllBytes method polyfill using FileStream with append mode
• Added unit test to verify the method works correctly
• Updated documentation to reflect the new polyfilled member

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
PolyShim/Net90/File.cs	Implements the AppendAllBytes method polyfill using FileStream in append mode with write access
PolyShim.Tests/Net90/FileTests.cs	Adds unit test for the new AppendAllBytes method
PolyShim/Signatures.md	Updates member count and adds documentation entry for the new polyfilled method

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (cc00c19) to head (38ef19d).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@     Coverage Diff      @@
##   master   #55   +/-   ##
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