[File Explorer Integration] Git submodule status and commit log inside submodule

[DefaultRyan]

Summary of the pull request

Parse submodule status (which submodules are new, changed, and/or dirty) and report latest commit info from files within the submodule.

Still to do: display folder and file status for submodule contents. That is coming next, but this commit is getting big enough as it is.

Detailed description of the pull request / Additional comments

A big part of this PR is the addition of test repos under the resources folder. This allows us to "freeze" a repository in a specific state, including the working directory and index. We're able to do this by renaming .git to dot-git and .gitmodules to dot-gitmodules, and this makes Git see these files/folders as just normal stuff, instead of special Git infrastructure. When deploying the repo to a temp location for testing, we undo that rename. This approach was inspired by similar approaches seen in libgit2 and libgit2sharp for their unit testing.

When finding the latest commit, always run the git command from the leaf-most folder. This way, git will automatically use the correct history when were are inside a submodule.

Parse submodule-specific status and provide the appropriate property values. New submodule status values are:

• Submodule staged
  • The submodule has been added, and this addition is staged.
• Submodule changed
  • This repository's submodule is pointing to a different commit than the superproject's submodule.
• Submodule dirty
  • Files have been changed in the submodule's index or working directory.

Validation steps performed

Ran newly added unit tests.

PR checklist

• Tests added/passed
• Documentation updated

[ssparach]

May we consider using a more descriptive method name instead of TryAdd which is identical to the called Dictionary method name? Thanks!

[DefaultRyan]

I deliberately chose TryAdd because it is identical to the method on Dictionary. My hope was that would make the semantics clear.