Handle `test_per_src` modules as indirect dependencies in APEXes.

In `apex.apexBundle.GenerateAndroidBuildActions`, we used to pass the
"all tests" ("") module as `module` for all `apexFile` objects created
from a test module using `test_per_src: true`.  An immediate issue of
this situation was that the "" module is hidden from Make, which made
all the generated `apexFile` objects hidden from Make too. This would
break the construction of flattened APEXes, as they rely on Make logic
to install their files.

Instead of collecting `test_per_src` test variations' output files in
`cc.Module.GenerateAndroidBuildActions` and using them in
`apex.apexBundle.GenerateAndroidBuildActions` as part of handling the
"" variation as a direct dependency of an `apexBundle`, process them
as indirect dependencies (and do nothing for the "" variation direct
dependency).

Adjust the indirect dependency logic in
`apex.apexBundle.GenerateAndroidBuildActions` to allow not only
shared/runtime native libraries as indirect dependencies of an
`apexBundle`, but also `test_per_src` tests.

Test: m (`apex/apex_test.go` amended)
Bug: 129534335
Change-Id: I845e0f0dd3a98d61d0b7118c5eaf61f3e5335724