[rush-lib] Normalize plugin autoinstaller file line endings

[kevin-y-ang]

Summary

• Update AutoinstallerPluginLoader.ts to read source JSON files and write them with convertLineEndings: NewlineKind.Lf.
• Apply this behavior to both the plugin manifest and optional command-line JSON file.

Details

• At TikTok we develop on Mac. When running rush update, AutoinstallerPluginLoader.ts will the line endings of rush-plugin-manifest.json and command-line.json. This creates unstaged changes that causes confusion and inconvenience for developers.
• This behavior eists because FileSystem.copyFile() does not support the option convertLineEndings: NewlineKind.Lf. This problem can be resolved by reading the file into memory with FileSystem.readFile() and writing it with FileSystem.writeFile() with the convertLineEndings: NewlineKind.Lf option.

How it was tested

• Testing it on TikTok repos, this removes the issue of Rush changing the line endings of rush-plugin-manifest.json and command-line.json when running rush update.

[octogonz]

Will this create the opposite problem on Windows?

I wonder if NewlineKind.OsDefault: is better or worse than NewlineKind.Lf. 🤔

@dmichon-msft @iclanton

[kevin-y-ang]

It seems like NewlineKind.Lf is the default option across the codebase, appearing 11 times. On the other hand, NewlineKind.OsDefault appears 2 times.