Fix spacing and colors related to All Apps header

* Add space above personal/work tabs: `all_apps_header_top_margin`.
* Prevent search results from being cut off at the top:
  `all_apps_header_bottom_padding`.
* Update header height calculations based on code/xml examination and
  observations of actual margins and padding.

Test: Manual: Check consistent behavior of spacing and header colors
in different conditions that are affected by this change:
1. Apps: Many installed (scrollable), and few (not scrollable).
2. Work profile: With and without one.
3. Search results.
4. Font size settings, smaller and larger.
5. (No known impact) Display size settings, smaller and larger.
6. Home screen rotation enabled, in landscape and portrait.

Issue: calyxos#1260
Change-Id: I5cbf47eb4a734e9ce9b42d8ef9a27a167d614da0