fixes #46826

Update src to build with TS 2.7

Explicitly assign this.message in the else body

fixes #40229

fixes #38393

fixes #32739

fixes #30057

We are passing `GitErrorData` to `JSON.stringify` to include in the string
generated by `GitError.toString`. However, we set `replacer` to `[]`, which
means `JSON.stringify` will _always_ serialize to `{ }`. After this change
GitError messages should be more understandable, and not just say `Failed to
execute git`.

Scan for submodules when a module is added, and add those repositories immediately.

If the classic GitHub for Windows (creatively named github.exe) is installed alongside the new GitHub Desktop (which installs a github.bat file to PATH), we can get into the situation where Code can ask the GUI to authenticate for a private repository, which it doesn't understand.