DevTools: [Documentation] Add syntax highlight for code examples

Drive-by fixes:
1) Move DOMSyntaxHighlighter to ui/
2) Remove "CSS" from experiment name
3) Fix documentation for RegExp methods

BUG=391593

Review URL: https://codereview.chromium.org/530003002

git-svn-id: svn://svn.chromium.org/blink/trunk@181468 bbb929c8-8fbe-4397-9dbb-9b2b20218538