Add ctrl-w _ and ctrl-w = (#21227)

Closes #ISSUE

Release Notes:

- vim: Add support for `ctrl-w _` and `ctrl-w =`

assets/keymaps/vim.json

@@ -561,6 +561,8 @@
       "ctrl-w <": ["vim::ResizePane", "Narrow"],
       "ctrl-w -": ["vim::ResizePane", "Shorten"],
       "ctrl-w +": ["vim::ResizePane", "Lengthen"],
+      "ctrl-w _": "vim::MaximizePane",
+      "ctrl-w =": "vim::ResetPaneSizes",
       "ctrl-w g t": "pane::ActivateNextItem",
       "ctrl-w ctrl-g t": "pane::ActivateNextItem",
       "ctrl-w g shift-t": "pane::ActivatePrevItem",