Reapply "Convert overrides to a TransitionMutator"

Replace the performOverrideMutator with a TransitionMutator.

This relands I358f260f1bcd894d7803036ce77ba666c0429355, which was
reverted due to a subtle behavior change when converting AliasVariation
into an IncomingTransition.  AliasVariation is temporary, losing its
effect after the next call to CreateVariations that doesn't also call
AliasVariation.  dexpreopt_bootjar.go was checking if a variant existed
after the apex mutator had run and obsoleted the alias created by the
perform_override mutator.  When the alias was replaced by
IncomingTransition it wasn't obsoleted and dexpreopt_bootjar.go found
extra dependencies.  The extra dependencies were picked up by the
core licensing code walking dependencies, and caused a significant
increase to the size of system/etc/NOTICE.xml.gz.

ag/27324277 removed flags that triggered the extra dependencies,
which prevents the system/etc/NOTICE.xml.gz increase for now.
b/340911730 tracks avoiding the unnecessary dependencies if the
flags are re-enabled.

Bug: 319288033
Flag: NONE
Test: all soong tests pass
Test: no change to build.ninja
Change-Id: I46171ba69f24482414a20d63a131941a162f025c