Add a lint baseline for Launcher3

The lint version in tm-qpr-dev incorrectly flags BaseActivity.java.
Add an entry to lint-baseline.xml file to silence the incorrect
error.  The newer version of lint in master doesn't have the false
positive.

Bug: 258754271
Bug: 256019562
Test: m RUN_ERROR_PRONE=true javac-check lint-check
Change-Id: I2fd22e96c8e89b7dc25132089e36d599e012e747
Merged-In: If02f87ef74c73321afa3427d845ad80539292b30