Add git commit fallback for repositories without changelog files

[vaind]

Summary

• Adds fallback to generate changelog from git commits when no changelog.md exists
• Refactors code into separate functions for better maintainability
• Supports repositories like Catch2, React, Vue.js that use GitHub releases instead of changelog files

Details

This PR enhances the get-changelog.ps1 script to work with GitHub repositories that don't maintain a traditional CHANGELOG.md file (like Catch2).

Key Changes:

1. Git Commit Fallback: When no changelog files are found, the script now clones the repository and extracts commit messages between the specified tags
2. Code Refactoring: Split the monolithic script into focused functions:
   • Get-ChangelogFromCommits: Generate changelog from git log
   • Get-ChangelogFromDiff: Generate changelog from file diff (existing logic)
   • Format-ChangelogContent: Apply consistent formatting and sanitization
3. Improved Link Handling: Same link sanitization (github-redirect.dependabot.com) applied to prevent notifications
4. Version Filtering: Automatically filters out version tag commits (e.g., "v3.10.0") to focus on meaningful changes

Example Output:

For repositories without changelog files, the output now looks like:

## Changelog

### Commits between v3.9.1 and v3.10.0

- Forbid deducing reference types for m_predicate in FilterGenerator ([#3005](https://github-redirect.dependabot.com/catchorg/Catch2/issues/3005))
- Make message macros (FAIL, WARN, INFO, etc) thread safe
- Improve performance of writing XML
- Improve performance of writing JSON values
- Handle DESTDIR env var when generating pkgconfig files
- Fix color mode detection on FreeBSD by adding platform macro
- Don't add / to start of pkg-config file path when DESTDIR is unset

Test plan

• All existing tests continue to pass
• Added 4 new tests covering the git commit fallback functionality
• Verified works with Catch2 repository (no changelog.md)
• Confirmed link formatting prevents GitHub notifications
• Tested edge cases (no commits, same tags, version filtering)

🤖 Generated with Claude Code

[github-actions]

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[vaind]

@sentry review

[vaind]

Thank you for the detailed review! I've addressed all the feedback:

✅ Fixed Issues:

🔴 Critical Error Handling

• Added comprehensive error handling for all git operations (git clone, git fetch, git log) using the same pattern as git diff
• Fixed PSNativeCommandErrorActionPreference termination by wrapping git commands with $ErrorActionPreference = 'Continue' in try/finally blocks
• Added specific exit code reporting for better debugging

🟡 Robustness Improvements

• Progressive fallback strategy: shallow clone (200) → deep clone (1000) → full clone if needed
• Guaranteed cleanup using try/catch/finally blocks with explicit repository directory removal
• Better error messages with specific exit codes and clearer warnings

🧪 Test Reliability

• Made tests more robust by checking structure/patterns rather than exact content to reduce external dependency brittleness
• Added error handling test for invalid repositories to verify graceful failure
• All 16 tests pass including new error scenarios

🔧 Key Changes Made:

# Before: Could cause script termination
git clone --depth=200 $repoUrl $repoDir

# After: Proper error handling with fallbacks
$cloneResult = & {
    $ErrorActionPreference = 'Continue'
    try {
        git clone --depth=200 $repoUrl $repoDir
        # + progressive fallback logic
    } finally {
        $ErrorActionPreference = $oldErrorActionPreference
    }
}

The implementation now handles all error scenarios gracefully while maintaining the performance benefits of shallow clones when possible.

All CI tests continue to pass ✅

[vaind]

@sentry review