Make Color inversion shortcut searchable

The color inversion shortcut is not searchable because this preference
is dynamically created. In order to make it searchable, we should add
index raw data for this preference.

Fixes: 223514734
Test: manual test
1) Open Settings search
2) Search for shortcut
3) check that the search results have Color inversion shortcut

Change-Id: I354d0c0e63cc12bd5012d7f26a165278a40bcf2d