Add keyboard shortcuts for the prompts on Linux (#13915)

This change adds ability to choose any action from prompts, not just the
default one and cancel as Zed has right now. For example, when a user
tries to close a file with edits in it the prompt offers "Don't save"
option that can be selected only with mouse. Now you can use arrows,
tab/shift-tab to pick action and enter/space to confirm it.

Fixes [#13906](https://github.com/zed-industries/zed/issues/13906)


Release Notes:

- Added keyboard navigation in the prompts on Linux
([#13906](https://github.com/zed-industries/zed/issues/13906)).


Co-authored-by: Thorsten Ball <mrnugget@gmail.com>

assets/keymaps/default-linux.json

@@ -3,10 +3,14 @@
   {
     "bindings": {
       "up": "menu::SelectPrev",
+      "shift-tab": "menu::SelectPrev",
+      "home": "menu::SelectFirst",
       "pageup": "menu::SelectFirst",
       "shift-pageup": "menu::SelectFirst",
       "ctrl-p": "menu::SelectPrev",
       "down": "menu::SelectNext",
+      "tab": "menu::SelectNext",
+      "end": "menu::SelectLast",
       "pagedown": "menu::SelectLast",
       "shift-pagedown": "menu::SelectFirst",
       "ctrl-n": "menu::SelectNext",