Update the search button to be a text+image selector.

- Search selector now fills up the entire width of the Toolbar (minus the
  other action buttons)
- Clicking the search selector simply brings up the Search fragment, like
  before (the selector itself is not an EditText).
- Put the SearchView into xml, as a child of the Toolbar, instead of a
  menu action item.
- Updated the SearchView to fill up the width of the Toolbar when it
  becomes enabled.

Bug: 73576
Change-Id: Ie0f86429fdae95263fc5e1b53ab19f2e7f73a933