Use correct regex for javadoc tag with optional description

Also fixes instances of missing @RestrictTo in compat/ directory.

Previous CLs were tested against commits rather than files, so they
returned false positives (and negatives). This one was correctly run
against the entire compat/ directory.

Bug: 33462608
Test: ran checkstyle on compat
Change-Id: I7b194bb2dbf971bf1a1306794a4b2cdf554e4e02
6 files changed