apex: pass "apex name" as literal to apex variants

When a cc module sets UseApexNameMacro(mutated property), it is built
with __ANDROID_APEX_NAME__ for its apex variants.

For now the new prop is used by aidl_interface-generated modules only.

Note that we already have __ANDROID_APEX_<NAME>__ macro. The new macro
can be used when we need to pass the name as data while the old one is
useful when we want conditional compilation.

Bug: 165017590
Test: m com.android.aidltest
     check build.ninja if -D__ANDROID_APEX_NAME__ is defined for apex
     varaints
Change-Id: Ia81ba8f833d23254e58c9777daf184d7861f07a7