Make CloseAll keybindings more closely match VS Code (#28060)

Changes default keymaps to more closely match the behavior of VSCode.

New Zed behavior:
`cmd-k w` / `ctrl-k w` -- Closes all buffers in the current pane
`cmd-k cmd-w` / `ctrl-k ctrl-w` -- Closes all buffers in all panes

VScode:
`cmd-k cmd-w` is workbench.action.closeAllEditors (close all buffers in
all splits)
`cmd-k w` is workbench.action.closeEditorsInGroup (close all buffers in
current split)

Both leave pinned tabs untouched.

Release Notes:

- Improved keybindings for close all tabs to better match VSCode
behavior

assets/keymaps/default-linux.json

@@ -311,6 +311,7 @@
       "ctrl-k t": ["pane::CloseItemsToTheRight", { "close_pinned": false }],
       "ctrl-k u": ["pane::CloseCleanItems", { "close_pinned": false }],
       "ctrl-k w": ["pane::CloseAllItems", { "close_pinned": false }],
+      "ctrl-k ctrl-w": "workspace::CloseAllItemsAndPanes",
       "back": "pane::GoBack",
       "ctrl-alt--": "pane::GoBack",
       "ctrl-alt-_": "pane::GoForward",

assets/keymaps/default-macos.json

@@ -430,7 +430,8 @@
       "cmd-k e": ["pane::CloseItemsToTheLeft", { "close_pinned": false }],
       "cmd-k t": ["pane::CloseItemsToTheRight", { "close_pinned": false }],
       "cmd-k u": ["pane::CloseCleanItems", { "close_pinned": false }],
-      "cmd-k cmd-w": ["pane::CloseAllItems", { "close_pinned": false }],
+      "cmd-k w": ["pane::CloseAllItems", { "close_pinned": false }],
+      "cmd-k cmd-w": "workspace::CloseAllItemsAndPanes",
       "cmd-f": "project_search::ToggleFocus",
       "cmd-g": "search::SelectNextMatch",
       "cmd-shift-g": "search::SelectPreviousMatch",