LayoutLib: Support getting resource arrays.

- Don't crash when Resources.get<Type>Array() is called.
- If the IDE supports it, actually return the value.
- Add tests for getArray.
- Update test app to latest gradle plugin version.
- Switch to using AppTheme for tests, since the tests depend on some
  custom theme attributes. The AppTheme now inherits from
  Material.Light.DarkActionBar, so other tests should be unaffected.

Depends on a newer version of sdk-common, which fixes the parsing of
array resource in value files.

Bug: 12372031
Change-Id: I313b61511e98ac1402d75056ebfdeeb005ebb96d