Use LexemeIdHtmlFormatter if format is 'text/html; disposition=diff'
The formatter-factory-callback was using the default EntityIdFormatter
when not of SnakFormatter::FORMAT_HTML_VERBOSE or FORMAT_HTML instead
of the nice LexemeIdHtmlFormatter.
We should also use the LexemeIdHtmlFormatter when FORMAT_HTML_DIFF
Add test to LexemeDiffVisualizerIntegrationTest.php
Bug: T195511
Change-Id: I36f31f6440715b62aefdc26a504f5cb1c4f0e1d9