Fix dumpOatRules.

This method generates a build rule that runs oatdump for debugging
purposes.

- Pass "--runtime-arg -Xgc:CMC" to oatdump if UFFD GC is enabled.
- Build the phony name from the image name to avoid conflicts when using
  this method for multiple boot images.

Bug: 290583827
Test: m dump-oat-boot
Change-Id: I7adc97cb85b571486b78f173fb80ff7da2c4bfe4