Splits models into its own file

GitLens uses legacy project routes for GitLab:

- `${projectURL}/branches`
- `${projectURL}/tree/${branch}`
- `${projectURL}/commit/${sha}`
- `${projectURL}/compare/${base}${notation}${compare}`
- `${projectURL}/blob/${ref}/${fileName}`

These routes are all deprecated and scheduled for removal. See these references:

- https://docs.gitlab.com/ee/development/routing.html#project-routes
- https://gitlab.com/gitlab-org/gitlab/-/issues/118849
- https://gitlab.com/gitlab-org/gitlab/-/issues/28848

This change replaces them with the following scoped routes:

- `${projectURL}/-/branches`
- `${projectURL}/-/tree/${branch}`
- `${projectURL}/-/commit/${sha}`
- `${projectURL}/-/compare/${base}${notation}${compare}`
- `${projectURL}/-/blob/${ref}/${fileName}`

See also: https://github.com/microsoft/vscode/issues/85930

Only get stats if isDirectory is null

Increases the width of the heatmap gutter glyph
Moves gutter glyphs closer to the code

Adds line fading option to heatmap annotation

And separates the existing Gerrit provider to a new GoogleSource one.

Closes #1953

Adds a GitLens features section to help avoid GitLens+ feeling like a gate

With Node 16, `Intl.DateTimeFormatOptions` seems to no longer honor the `dayPeriod` option and always return the "long" version, so fallback to use the `timeStyle` option if needed