fix: resolve symlinks when checking which files to format

[nfvs]

Description

Currently find_project_root() resolves symlinks, but get_sources() doesn't, so trying to format a file that contains symlinks will fail:

$ python -m black --check /home/nfvs/code/black/src/black/files.py
No Python files are present to be formatted. Nothing to do 😴

This commit changes methods used in get_sources() to, like find_project_root(), use Path.resolve() instead of Path.absolute(), which will follow symlinks.

Also fixes:

• Black formatter does not format symlinked files (Black 24.1.1) microsoft/vscode-black-formatter#444
• black ignores file in current folder if current folder is git workspace and (parent of) current folder is a symbolic link #4205

Checklist - did you ...

• Add an entry in CHANGES.md if necessary?
• Add / update tests if necessary?
• Add new / update outdated documentation?

[github-actions]

diff-shades reports zero changes comparing this PR (689ecad) to main (dab37a6).

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What is this? | Workflow run | diff-shades documentation

[nfvs]

Test failures may be due to another bug: #3552

[hauntsaninja]

Thanks for the PR, but the tests that are failing test important behaviour. Do you have a small repro of the case where you want current behaviour to be different?

[hauntsaninja]

If you get a moment, would you mind testing #4222 and see if it works for your use case?

[nfvs]

If you get a moment, would you mind testing #4222 and see if it works for your use case?

@hauntsaninja It does fix it, I'll close this PR. Thanks!