Verify the possibility of adding a file duplication check to soong

Patch merged.

Although the patch is already approved, Stephen Hines wanted to double check a few things. It’s been 3 weeks, so I pinged him and I’m waiting for a response.

Upstream review: https://android-review.googlesource.com/c/platform/build/+/2467321

Patch sent to Google. If they think it’s interesting to add it to the build system, I’ll submit to AOSP upstream.

It is possible to add a script to the build system. As long as the commands used in the script are in the allowed list in PathConfigin build/soong/ui/build/paths/config.go, it should run.

The build system creates the rules from build/make/core/Makefile, so the script must be included in a target that depends on the file system image being generated. Soong will use this Makefile to generate a ninja file and the build will run as usual.

If we were to submit such a check to AOSP, I think it would be best to avoid changing the list of allowed commands, or at least not add anything that might be controversial in there (i.e. impacts security or reproducibility of builds).