This repo uses protoc for verification -- to make sure that things like options interpretation and source code info match what the reference compiler produces.

This updates the version of protoc used to the latest release v22.0. This uncovered discrepancies: changes/fixes in protoc that required changes to protocompile code to match.

1. The first failing test to address was in the canonical output for options when an override version of descriptor.proto was in use. The new v22.0 compiler includes a new field on google.protobuf.EnumOptions with a tag of 6. It just so happens that the test's override version also had a field with a tag of 6. The new compiler's field is a bool, but the override version's is a string. Since these use incompatible wire type encoding, protoc treats the override field as an unrecognized field, despite it having a known tag. So I've updated the options interpretation code to implement the same logic.
2. The next set of tests to address were known changes coming in the new compiler: fixes to source code info. So the changes here address a couple of TODOs in the code. I've also added some more comments to a test file, to provide some more scenarios in which to verify that protocompile generates the same source code info as protoc.