An ActionSet doesn't need to walk the graph.

Resolutions map back to the root, but actions do not. An iteration
works just fine.

Simplify TargetNodeSet so that it is directly iterable.

Bug: 261787132

Test: m droid dist compliance_dumpgraph compliance_dumpresolutions \
        compliance_sbom compliance_listshare compliance_rtrace \
        compliance_checkshare xmlnotice textnotice htmlnotice \
        compliancenotice_shippedlibs compliancenotice_bom

Test: m compliance_checkshare cts && \
        out/host/linux-x86/bin/compliance_checkshare out/host/linux-x86/gen/META/lic_intermediates/out/host/linux-x86/cts/android-cts.zip.meta_lic

Change-Id: Ic5a2d809b5a9a47b5d85f61e3a4a790dbe8f5fd2