Batch cquery requests for mixed builds

This adds an extra step to mixed builds: creating a master BUILD/bzl
file pair to facilitate running a single cquery command to analyze
all soong->bazel edges in a single request.

Test: Mixed build tested with aosp/1441774, verified ninja outputs
depend on `bazel-out/` intermediates
Test: Manually verified contents of master BUILD and bzl files

Change-Id: I04803bcc91ac4182578f505b3f42893061ddd167