neovim: support clicking targets about cursorless HOT 3 OPEN

gx			Opens the current filepath or URL (decided by
			|<cfile>|, 'isfname') at cursor using the system
			default handler, by calling |vim.ui.open()|.

							*v_gx*
{Visual}gx		Opens the selected text using the system default
			handler, by calling |vim.ui.open()|.

vim.ui.open({path})                                            *vim.ui.open()*
    Opens `path` with the system default handler (macOS `open`, Windows
    `explorer.exe`, Linux `xdg-open`, …), or returns (but does not show) an
    error message on failure.

    Expands "~/" and environment variables in filesystem paths.

    Examples: >lua
        -- Asynchronous.
        vim.ui.open("https://neovim.io/")
        vim.ui.open("~/path/to/file")
        -- Synchronous (wait until the process exits).
        local cmd, err = vim.ui.open("$VIMRUNTIME")
        if cmd then
          cmd:wait()
        end
<

    Parameters: ~
      • {path}  (`string`) Path or URL to open

    Return (multiple): ~
        (`vim.SystemObj?`) Command object, or nil if not found.
        (`string?`) Error message on failure, or nil on success.

    See also: ~
      • |vim.system()|