Enforce whitespace consistency in maintained files

[alex-thiessen-for-siemens]

Summary

This standalone cleanup is motivated by the incidental whitespace changes mixed into #1488. It normalizes the existing maintained-file baseline and adds a permanent check so future semantic PRs do not need to carry unrelated whitespace edits.

Policy

• No trailing spaces or tabs.
• Each line uses LF as its end-of-line character.
• Non-empty files end with exactly one final LF.
• The vendored test/googletest-1.16.0/ tree is excluded.

The cleanup normalizes maintained text to LF and leaves the vendored tree unchanged. You may run python3 util/check-whitespace.py to check whitespace before submitting a pull request.

CI

The new Whitespace workflow runs on pushes, pull requests, and manual dispatch. Please add the Whitespace check to the required status checks for master after this workflow is available. This account does not have permission to change the upstream branch rules.

This PR intentionally does not modify or comment on #1488.

[SGSSGene]

This is awesome! Thank you!

May I ask, which files end in CRLF? the only two that I can find are yaml-cpp.natvis and yaml-cpp.natvis.md

This should definitely be also fixed and changed to LF.

I would say the policy is:

• No trailing spaces or tabs.
• Each line ends with a newline (LF)
• The vendored test/googletest-1.16.0/ tree is excluded.

[SGSSGene]

This is great!

I would like to pin it down to only LF symbols.
And even though it is called a 'newline' character, I think it is easier/better to think of it as a 'end of line' character, which makes it very clear when/how to use it and why there has to be one at the end of a non-empty file.

[SGSSGene]

@jbeder I think this is a great change to keep maintain cleanliness of all files which reduces noise in PRs for whitespaces. This needs your approval and intervention to add there CI workflow as an requirement for PRs to pass.

[alex-thiessen-for-siemens]

Addressed. src/contrib/yaml-cpp.natvis and src/contrib/yaml-cpp.natvis.md were the only maintained files using CRLF; both now use LF. The policy and checker require LF for maintained text, while the vendored test/googletest-1.16.0/ tree remains excluded. Making Whitespace a required status check still needs an upstream maintainer with branch-rule permissions.

[alex-thiessen-for-siemens]

Initially, I decided that natvis-related files should remain CRLF, as these are for Windows users only. Hope Visual Studio can deal with LF natvis, else an exception to the EOL check would be needed.