Set up protobuf conformance tests

[Mr3zee]

Subsystem
Protoc-gen

Problem Description
Google publishes conformance tests for protoc-gen language implementations to test functionality

Solution
Setup our conformance tests:

• Added runner executable dependency
• Added conformance protos and generated code to the repository to track changes
  • Only proto3 are generated due to GROUPS unsupported in protoc-gen
• Added junit tests to mimic conformance tests
• Fixed:
  • Generation for single package in path
  • Logging in protoc-gen plugins
  • Package names
  • Enums in repeated fields
  • Gradle plugin lazy tasks creation order
  • Gradle plugin initialization order bug
  • packed enum generation
  • boolSize function
  • Well-Known types
  • Explicit API mode

Current test status:

=== Conformance Test Results ===
Total baseline tests:   5545
[+] Passed tests:       1188
[-] Failed tests:       4357

Details:

There are 2934 Proto3 tests (+editions), out of them 1188 pass, 1746 fail. But from failing, only 208 are tests with Protobuf input and output, and rest are Json
So actually we do 1188/1396 tests, which is 85%*!

*of tests we intended to support initially, so excluding Json and only taking Proto3 and Editions_Proto3