Build/Test Tools: Ignore EOL differences in tests using multiline string assertions.

Unix vs. Windows EOL style mismatches can cause misleading failures in tests using the heredoc syntax (`<<<`) or multiline strings as the expected result.

Fixes #31432. See #42594, #47411.
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git-svn-id: https://core.svn.wordpress.org/trunk@46409 1a063a9b-81f0-0310-95a4-ce76da25c4cd