license metadata reverse trace

Introduce the below command-line tool:

rtrace outputs a list of targets and conditions causing one or more
projects or target nodes to require sharing to resolve a restricted
condition.

Bug: 68860345
Bug: 151177513
Bug: 151953481
Bug: 213388645
Bug: 210912771

Test: m all
Test: m systemlicense
Test: m rtrace; out/soong/host/linux-x85/rtrace -rtrace=...

where ... is a project or license metadata file followed by the path to
the .meta_lic file for the system image. In my case if

$ export PRODUCT=$(realpath $ANDROID_PRODUCT_OUT --relative-to=$PWD)

... can be expressed as:

system/core ${PRODUCT}/gen/META/lic_intermediates/${PRODUCT}/system.img.meta_lic
or
${PRODUCT}/gen/META/lic_intermediates/${PRODUCT}/system.img.meta_lic ${PRODUCT}/gen/META/lic_intermediates/${PRODUCT}/system.img.meta_lic

Change-Id: I40a0586699d9b8a8dd2bd4ba26756c9649ebf964