Adds support for a whitelist of allowed .git projects in BindOverlay.

This allows using a whitelist of allowed projects in the sandbox,
where any .git project not in this list is excluded from bind mounts.

Test: Build a target in NSJail using an allowed projects list equal to
that target's split manifest projects.
Test: test.sh
Bug: 156639642
Change-Id: I16ad22402e5e83982f157ef6e366140a3f31d65b
2 files changed