vim: Add support for <count>gt and <count>gT (#38570)

Vim mode currently supports `gt` (go to next tab) and `gT` (go to
previous tab) but not with count. Implement the expected behavior as
defined by vim:

- `<count>gt` moves to tab `<count>`
- `<count>gT` moves to previous tab `<count>` times (with wraparound)

Release Notes:

- Improved vim `gt` and `gT` to support count, e.g. `5gt` - go to tab 5,
`8gT` - go to 8th previous tab with wraparound.

assets/keymaps/vim.json

@@ -95,8 +95,8 @@
       "g g": "vim::StartOfDocument",
       "g h": "editor::Hover",
       "g B": "editor::BlameHover",
-      "g t": "pane::ActivateNextItem",
-      "g shift-t": "pane::ActivatePreviousItem",
+      "g t": "vim::GoToTab",
+      "g shift-t": "vim::GoToPreviousTab",
       "g d": "editor::GoToDefinition",
       "g shift-d": "editor::GoToDeclaration",
       "g y": "editor::GoToTypeDefinition",