Replace the library for interacting with git

Problem to solve

The extension is currently using execa npm module to invoke git shell command and then parse the stdout lines to get information.

This results in increased effort and complexity when interacting with git repository. This approach caused several bugs in the past (#193 (closed) #197 (closed)).

Proposal

Replace the custom solution with a dependency. Either npm module like simple-git, or with the API exposed by git official VS Code Extension (this is the approach taken by !54 (closed) )

Further details

The current custom implementation is in src/git_service.js

Links / references

• Example implementation use of simple-git: https://gitlab.com/viktomas/gitlab-example-extension/-/blob/master/src/gitService.ts#L28-43
• MR connecting to the git extension API: !54 (closed)