Verify updated font is used in app process.

This CL adds a VTS test that:
1. Updates NotoColorEmoji font
2. Launches a test app that renders an emoji
3. Verifies that the updated NotoColorEmoji font file is used by the app
   process.

Bug: 180370569
Test: atest UpdatableSystemFontTest
Change-Id: I418d7cc23a290ebe4ae6e5b8af782b336497fbdd