HostStubGen: Write verbose/debug log to a file

See below for the log filename.

Also disable an unimplemented flag.

Bug: 311174191
Test: ./scripts/run-all-tests.sh
Test: m framework-minus-apex.ravenwood
    and examine console output and
    out/soong/.intermediates/frameworks/base/framework-minus-apex.ravenwood-base/android_common/gen/hoststubgen_framework-minus-apex.log
Change-Id: I9997370c93e2fe90276d5f3e657d45d440ca0a59