Convert apex modules to app bundle modules

Convert .apex files to base.zip files suitable for bundletool.
They will be copied to the dist directory when built with
TARGET_BUILD_APPS and dist.

Also fix up apex.go to use Build instead of the deprecated ModuleBuild,
and ctx.ModuleName() instead of module.ModuleBase.Name().

Bug: 117295826
Test: tapas com.android.runtime && m dist
Change-Id: I7919c8d3da280e87c624a6628a1715e8060852dc