This fixes an incremental build issue where we didn't clean up old aidl
header files (or necessarily notice that they were updated).
We do this by declaring the header files as outputs in the build graph,
but this means that the src file name needs to be convertible to the
aidl package name, as that's how the header file paths are created. In
many cases, filegroups can be used to strip path prefixes from the aidl
files.
Bug: 112114177
Test: treehugger
Change-Id: If534ff3dbfac329dea9a7402e30be74495754160
Compute sources including from filegroup and genrule dependencies
before determining if any sources will cause flags to be added.
Test: gen_test.go
Change-Id: I0434b003bbda07a58bb2ce1a0a72997918c8fae2
