Update most of Go native lang to be repoless

[DavidSGK]

We want to reduce dependencies when syncing/gen'ing for native lang. Similar to lekkodev/ts-tools#45, the changes here make things (mostly) repoless for Go.

Changes are messy and a bit hard to follow, but these are the general details:

• Updated deps to use new repository contents types from Add Namespace and RepositoryContents messages in feature package #458
• Updated syncer to output repository contents instead of only writing to local config repository
• Updated generator to be constructed from repository contents instead of only reading from local config repository
• Added utility functions for reading/writing repository contents from/to a local config repository
• Update existing Go gen/sync tests
• etc.

There's still some work left after this PR, but this felt like a sane pausing point after the critical Go-related changes:

• Updating TS generator to use repository contents
• Updating gen/sync/bisync commands to have clear controls on whether local repository is involved or not
  • As a followup, updating push/pull based on how we want those to behave with these changes
• Cleanup on constructor/function signatures that are a bit all over the place at the moment
• Cleaning up unused functions that were used for testing or outdated commands

[DavidSGK]

I needed to also add this file descriptor, otherwise the descriptors added in #453 break sync because they depend on it

[DavidSGK]

This replaces the removed test methods by running through all of the test cases but also adding an extra sync step to compare parsed repository contents.

[DavidSGK]

Syncer struct was simplified a lot since we no longer need a repository and start from a blank file descriptor set. It was also changed to be repo-based rather than namespace-based because the FDS is shared and needs to be updated across namespaces. This is why a bunch of methods now take an additional namespace arg.