Surface Windows build errors in non-verbose mode

[stuartmorgan]

Description

Makes Windows builds extract things that look like warnings and errors from stdout, where MSBuild sends all output, and reports them as errors to the logger (essentially making them behave as if they had gone to stderr). This means that native build failures will no longer be completely invisible in non-verbose mode.

Also fixes an existing warning so that it won't show up in every build: The custom step in the Windows template CMake to do the re-entrant Flutter step includes a dummy output file to force the step to run every time. This causes a warning from VS. Marking it SYMBOLIC to indicate that it's not a real output file causes CMake to generate that VS step with the output validation step disabled so that it won't warn.

Related Issues

Fixes #33583

Tests

I added the following tests: Tests the regex extraction against sample normal and error lines, and ensures that it properly finds only the latter.

Checklist

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Breaking Change

Did any tests fail when you ran them? Please read Handling breaking changes.

• No, no existing tests failed, so this is not a breaking change.
• Yes, this is a breaking change.

[stuartmorgan]

Having to always use verbose mode on Windows finally annoyed me one too many times.

[jonahwilliams]

Having to always use verbose mode on Windows finally annoyed me one too many times.

I guess that is how progress is made

[jonahwilliams]

LGTM