eliminate dynamic calls in package:protobuf

We've seen a lot of dynamic calls, adding to binary size, coming from package:protobuf.

These can be statically linted with `avoid_dynamic_calls`, and then removed.

Start by locating dynamic calls within package:protobuf and run the avoid_dynamic_calls lint to identify the affected code. Done means the reported dynamic calls have been removed and the lint passes; the issue names no specific files or tests.

Written by the indexing model from the issue text.