Include "soong" in sandboxed out paths

Previously, the path to built files in the sandbox would be
out/.intermediates/... instead of out/soong/.intermediates/....

After this cl, it will be out/soong/.intermediates/.... This makes
it more consistent with the non-sandboxed paths, which is easier for
developers.

CtsApkVerityTestDebugFiles is a genrule that's used to find the paths
to other modules. Developers were expected to build it, then copy all
the files listed in its output file to a temporary directory. Those
paths would be wrong before this change.

Bug: 307824623
Test: ./build/soong/tests/genrule_sandbox_test.py CtsApkVerityTestDebugFiles
Change-Id: Iadf9e3240a2c828567e46b6b02cc14004f30e8bf