feat(git): support detached working trees

[jamestrew]

closes #2595

Description

Adds support for detached working tree for git related pickers.
Closely follows the pattern utilized by gitsigns.nvim in lewis6991/gitsigns.nvim#600

eg use case:

require("telescope").setup({
  defaults = {
    git_worktrees = {
      {
        toplevel = vim.env.HOME,
        gitdir = vim.env.HOME .. "/.cfg",
      },
    },
  },
})

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list relevant details about your configuration

Tested the following pickers with detached/attached working trees and git worktrees.

• git_files
• git_status
• git_stash
• git_commits
• git_bcommits
• git_branches

[jamestrew]

@Subjective can you test this branch?

[Subjective]

@jamestrew It works great now, thanks!

[Subjective]

Okay, one issue I noticed is that an error occurs if you open a file belonging to one of the detached working trees when Vim's cwd is set to another git repo and use_file_path = true. (My intended use case was to bring up a dotfile's commit history when its buffer is active, even when the cwd is set to another git repo).

Edit: Wait actually, it seems like use_file_path=true doesn't work anymore even for files opened in a normal git repo.

[jamestrew]

Ahh thanks for catching that. Having dug deeper, I'm not sure use_file_path really ever worked but things should be better now.

[Subjective]

Everything seems to be working fine now, thanks!