Use pre-constructed tokenizer in escapeWikitext

Change-Id: Ide85983484f618a8f6f9947d99f75c4f84cc001d
Fix entity encoding pipe in nested tpl args

 * Regexp won't match the nested pattern. Uses the tokenizer instead.

 * Adds a test.

 * _rt/kowiki/안락역?oldid=12456953

Bug: 65871
Change-Id: I820ce099cf43587412b4a94fe08b039ecd41ecf0