Add a coverage suffix to avoid Ninja file regeneration.

This CL uses the environment variable, EMMA_INSTRUMENT to determine whether or not coverage is enabled. If coverage is enabled, it adds a bunch of suffixes to the files generated in out/soong/ folders.

This change reduces the build time by avoiding ninja regeneration when users simply switches from atest to atest --experimental-coverage, or vice versa, and no Android.bp changes are made.

Bug: 331444846
Test: Locally run m libc, and then EMMA_INSTRUMENT m libc twice, no ninja regenerations required. Compared the hash of out/target/product/vsoc_x86_64/ between the before-change repo and after-change repo. Only diff is the after-change directory contains an extra file `out/target/product/vsoc_x86_64/.installable_files` while the original directory has only `out/target/product/vsoc_x86_64/.installable_files.previous`, both files have the same hash.
Change-Id: I91eb1134ac552f47a40f3d5ddaab630d146b0773