New parserTests.php features

Features to support T89331 analysis:

• Support dwdiff for word-level diffing
• Add --mark-ws feature which produces cleaner diffs when line breaks differ
• Add optional normalization of parser test output, allowing significant differences to be separated from insignificant differences.

Change-Id: I0e151caad1f8b2f97bf20b219f26f3101be82506