Keymap changes for editor::JoinLines (#14136)

- Linux (default) add ctrl-shift-j
- Linux (default) remove ctrl-j
  - Conflicted with: `"ctrl-j": "workspace::ToggleBottomDock",`
- MacOS (sublime) add cmd-shift-j

assets/keymaps/default-linux.json

@@ -398,7 +398,7 @@
     "bindings": {
       "ctrl-shift-k": "editor::DeleteLine",
       "ctrl-shift-d": "editor::DuplicateLineDown",
-      "ctrl-j": "editor::JoinLines",
+      "ctrl-shift-j": "editor::JoinLines",
       "ctrl-alt-backspace": "editor::DeleteToPreviousSubwordStart",
       "ctrl-alt-h": "editor::DeleteToPreviousSubwordStart",
       "ctrl-alt-delete": "editor::DeleteToNextSubwordEnd",