Added DROP opcode support to ApfGenerator for immediate return.

This commit adds support for the "DROP" opcode to ApfGenerator. This
opcode allows the apf_interpreter to return with DROP immediately,
skipping over subsequent instructions.

* design doc: go/apf-v6-proposal

Bug: 293811969
Test: TH
Change-Id: I84f3f1b17506aa7d048ccd60ea97eb41bd6b5673
2 files changed