Add lint.suppress_exit_code attribute

The Android lint --exitcode parameter can be skipped using
ANDROID_LINT_SUPPRESS_EXIT_CODE. Expose a similar attribute to Java
modules to ignore the exit code.

This is useful for integration testing. It is possible to build
libraries that report an error when linted. Othewise, such module would
break the checkbuild target.

Bug: 302400088
Test: m nothing
Change-Id: I372c42184f40d25753a688c380c0c63e9758ca00