Only write soong_injection files if changed

This also fixes determinism of these files (by ensuring that bazel
requests and their configurations are sorted, as these are used in the
soong_injection file output)

Bug: 266983462
Test: Manually verified soong_injection files are the same among
multiple runs
Test: Unit test
Test: m nothing

Change-Id: I1568930549cff0bc5676825434cc448d16ebdd4e