Replace match with test and omit redundant String conversion in jest-diff

[pedrottimark]

Summary

• Rewrote condition with RegExp.test because String.match is equivalent to RegExp.exec which returns either null or an array, therefore first condition was always false.
• Removed explicit conversion with String constructor, because switch (aType) case 'string' and have already returned if expectedType !== getType(b) or string asymmetric matcher.

Test plan

• Deleted stripAnsi from 2 existing tests with toBe(null) assertion
• Added 2 tests for either a or b is one line. The test for a one line and b multi line failed first.

[github-actions]

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