Repo state store naming

[charisk]

Reviewed names used in the repo states store, models (data/domain) and mappers, and updated them to match conventions agreed.

• Renamed data types to be referred to as DTOs.
• Renamed mapping functions to use the DTO term but also to follow the same naming patterns.
• Renamed and moved files to match convention.
• Introduced an index file for the repo states store.
• Introduced mapping functions for the top level models.

This PR looks fairly big but the changes are pretty small and straight forward. Please review commit by commit to see the differences.

Checklist

N/A:

• CHANGELOG.md has been updated to incorporate all user visible changes made by this pull request.
• Issues have been created for any UI or other user-facing changes made by this pull request.
• [Maintainers only] If this pull request makes user-facing changes that require documentation changes, open a corresponding docs pull request in the github/codeql repo and add the ready-for-doc-review label there.

[robertbrignull]

All changes LGTM

The index.ts file is an approach I haven't seen us use before, but it makes sense to designate repo-states-store.ts as the canonical entry point to that whole directory.

[charisk]

All changes LGTM

The index.ts file is an approach I haven't seen us use before, but it makes sense to designate repo-states-store.ts as the canonical entry point to that whole directory.

FWIW we've been using it in a few places (e.g. https://github.com/github/vscode-codeql/blob/main/extensions/ql-vscode/src/common/index.ts). Probably something we should talk about standardising though (and making visible!)