Rewrite rendering of Vector simple search

* Do not emit different HTML for LTR and RTL (partially fixes
  bug 46947).
* Do not use <button> element to avoid IE6 and Firefox troubles
  (fixes bug 50660). Only one little one-line hack is necessary now.
* Implement simple search formatting client-side (site/user options
  only control adding id=simpleSearch on the search container, CSS
  does the rest).
* Make the search use the 'fulltext' mode by default (to make full
  functionality accessible; fixes bug 25127) and 'go' when search
  suggestions are enabled and working (JavaScript enabled and browser
  support okay), as the module handles fulltext search itself.
* Use appropriate tooltips on the buttons (fixes bug 24248).
* General CSS and HTML cleanup in related areas.
* Keep the old styles necessary for backwards-compatibility with
  cached HTML. Removing them in subsequent commit Ib9f59b6d.

Co-Authored-By: Bartosz Dziewoński <matma.rex@gmail.com>
Co-Authored-By: Derk-Jan Hartman <hartman.wiki@gmail.com>
Bug: 24248
Bug: 25127
Bug: 46947
Bug: 50660
Change-Id: I5fe0543e273aab4fbfb88f8ce933bc49872d4793