Sharesheet - Adjust dark mode colors for GAR

The background for dark mode dialogs is lighter than the pixel/gm2
grey 800 color, while the text is a bit darker. Manually adjust the
colors per UX's recommendations.

Bug: 132861725
Test: Visual inspection
Change-Id: Iaa65c69ed387165987c41d8e2e7843e86e909dcc
2 files changed