Add a context binding for repo-level information

### Is your feature request related to a problem? Please describe.

It is often useful to know where the _repo root_ is when creating files - sometimes because you need to add a repo- or workspace-level in the heirarchy, or because you need to know something about the source provider information. Surfacing that information as a bindable piece of context enables template authors to use that information for their own templates without having to resort to shelling out.

### Describe the solution you'd like.

We should define a new component GUID and implementation for the .NET CLI host that
* discovers the source control root of the CWD
* discovers source provider information similar to sourcelink
* provider name, if any
* primary upstream name, if any
* current commit identifier, if any
and makes this information bindable via the existing context-binding mechanism for use in other symbols.

### Additional context

_No response_