Improve CppAnalyzer load time by reducing Regex.Match calls.

[yuehuang010]

Improve load times by checking keywords before matching regex.

• String.Contains() is orders of magnitude faster than Regex.Match(). So on critical paths, quickly check if the keyword exists before running the regex.
• CppAnalyzer speed up at least 5x as many messages are misses.
• AddMessage speed up by 10%.