Describe the solution you'd like

Today the codegen for https://pkg.go.dev/go.temporal.io/api/proxy has a big switch statement built on recursive reachability from workflow service (and a couple of other places). This causes orphaned proto messages (i.e. ones not referenced in that object graph) to be missed. We should change the code generator to walk the file descriptors of the entire proto repo so we know we catch them all.

This goes along with #1809.