Export non-apex variants of modules to make

Currently, non-apex variants of modules that are in apexes are not
exported to make unless they're apex_available to the platform. This
means that you can't `m` those modules directly.

However, there is a workaround in the apex androidmk implementation that
emits make rules for the removed modules, but just redirects them to
build the apex itself. We want to remove that, but one of the problems
with doing so is that you can no longer `m` many modules afterwards.

To fix that, unhide the apex's dependencies from make. To ensure they're
not installed, call SkipInstall() on them, and update SkipInstall() to
be more strict by setting `LOCAL_UNINSTALLABLE_MODULE := true`.

Bug: 254205429
Test: Presubmits
Change-Id: Ib971981559f3b642ce6be8890679e994e1b44be0

android/apex.go

@@ -603,7 +603,7 @@ func CreateApexVariations(mctx BottomUpMutatorContext, module ApexModule) []Modu
 			// Do not install the module for platform, but still allow it to output
 			// uninstallable AndroidMk entries in certain cases when they have side
 			// effects.  TODO(jiyong): move this routine to somewhere else
-			mod.MakeUninstallable()
+			mod.SkipInstall()
 		}
 		if !platformVariation {
 			mctx.SetVariationProvider(mod, ApexInfoProvider, apexInfos[i-1])