Cleanup usages of Dex2oatDepTag

Creates a new deptag type for it so that it can implement the marker
interfaces that will exclude it from being added to the APEX and from
visibility enforcement. The latter is probably not an issue ATM because
the dependencies are added after visibility checks are enforced but
this code is undergoing lots of refactoring so that may change.

Bug: 177892522
Test: m nothing
Change-Id: Ibd167d557adec761a2e3eed78f4d334c40a04fb9