Improve SearchView & secondary text accessibility

Conforming to the current version of the Material.io spec:
- Secondary text opacity increased slightly from 0.54 to 0.60
- Hint opacity is increased to the same level as secondary opacity.
  - Also, hint pressed state no longer increases opacity (since the next
    higher tier of opacity is primary, this would be confusing).
- Expand padding on SearchView close button to have a size of 48x48

Bug: 141212776
Bug: 230697814
Test: CtsThemeHostTestCases.android.theme.cts.ThemeHostTest#testThemes
Test: "Verified textfield hint opacity increased in 'Talkback
tests 14: Single line edit field'"

Change-Id: I95a682c98a61e3d8ea0ff7f33c0bbd2a4267f67c