Backport 4236

[ytmimi]

Read the original file for comparing/detecting newline (#4236)

Closes #4097

The code base diverged enough where a simple cherry-pick wasn't possible, but implementing the logic to read the input file when NewlineStyle::Auto was simple enough to implement.

New tests were added to hopefully prevent regressions.

[ytmimi]

I want to note that the original PR removes code that this PR does not since they take slightly different approaches to how apply_newline_style is called / updated. I haven't looked too deeply into it, but I wonder if we can remove similar code after making these changes.

I was also wondering if we had any tests in test/source that used crlf newlines. I was thinking it might be a good idea to add at least one system test for this backport to ensure that we maintain the newline style of the original input text regardless of the platform when newline_style=Auto

[ytmimi]

because of updates made to apply_newline_style, there will be some minor conflicts with #5418 depending on which backport PR gets merged first.

[rustbot]

☔ The latest upstream changes (possibly #6823) made this pull request unmergeable. Please resolve the merge conflicts.