Support msys2 git (fix absolute paths)

[jvasileff]

msys2 git returns absolute paths like "/c/Users/johnv/...". Git for Windows returns absolute paths like C:\Users\johnv...". To support both (and likely Cygwin git as well), relative paths are requested from git and then made absolute with path.resolve().

This fixes #143165

To test, install both Git for Windows & msys2 git

• Git for Windows: https://gitforwindows.org
• msys2: https://www.msys2.org/#installation

After installing msys2, install msys2 git with pacman -S git.

Once both gits are installed, vscode git integration should work with either of the following User settings.json configs (vscode restart required when switching):

{
    "git.path": "C:\\Program Files\\Git\\cmd\\git.exe"
    //"git.path": "C:\\msys64\\usr\\bin\\git.exe"
}

[dpengr]

Is this merge request just waiting for review?

[tigerinus]

Who's the right person for PR approval?