Fix UI bugs for widget picker search.

- Mirror search icon in RTL (b/184162989)
- Fix spacing between edit text and cancel button, to make it consistent
with space between search icon and edit text. (b/183602001)
- Scroll to top on every search result. (b/183602001)
- Fix keyboard overlap on orientation change. This is fixed by clearing
text on edit text differently (b/184048899)

Test: Manually tested
Bug: 184162989
Bug: 183602001
Bug: 184048899
Change-Id: I72ed51e1968a55a3105bd8b389d1bbd74d50d8af