Allow disabling errorprone even when RUN_ERROR_PRONE is true

Some modules use -XepDisableAllChecks to disable errorprone.
However, this still causes them to be compiled twice when
RUN_ERROR_PRONE is true. Allow the new enabled property to
be set to false to disable errorprone entirely, so that those
modules are only compiled once.

Bug: 190944875
Test: New unit tests
Change-Id: Ie68695db762fffcaf11bbbcb0509c4fcab73f5c5