Document str.replaceAll. Fix unit test to catch all built-in methods.
Document str.replaceAll. Fix unit test to catch all built-in methods.

GITHUB_BREAKING_CHANGES=N/A

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=357991272

google/closure-templates,google/closure-templates,google/closure-templates,google/closure-templates,google/closure-templates