v0.7.3: Standalone Golang generator templates

Tested with webrpc-gen v0.7.0. ✅

This version of Golang generator spits out generated code that is fully backward-compatible with webrpc-gen v0.6.0.

Previous versions (v0.7.0, v0.7.1, v0.7.2) had few minor bugs with go.field.type meta support (rendered some extra pointers incorrectly).