Add missing ctrl-shift-g binding for editor::UndoSelection to the JetBrains/IntelliJ keymap on macOS (#51130)

Daniel Eichman created

## Description:

This PR adds the missing `ctrl-shift-g` binding for
editor::UndoSelection to the JetBrains/IntelliJ keymap on macOS.

## Problem

In IntelliJ IDEA, when using multiple cursors:
- ctrl+g (macOS) adds the next occurrence to the selection
- ctrl+shift+g (macOS) removes the last added occurrence from the
selection

The current Zed JetBrains keymap has `ctrl-g` for SelectNext but is
missing the corresponding `ctrl-shift-g` for undoing/removing the last
selection.

## Reference

- Press Ctrl+G (macOS) to find and select the next occurrence
[link](https://www.jetbrains.com/help/idea/multicursor.html#multiple_words)

- To remove selection from the last selected occurrence, press
Ctrl+Shift+G (macOS)
[link](https://www.jetbrains.com/help/idea/multicursor.html#multiple_words)


This change improves parity with IntelliJ for users transitioning to
Zed.


### Demo 

https://github.com/user-attachments/assets/0c7f699f-697d-4b81-a929-53f765d254d8

Closes #ISSUE




Before you mark this PR as ready for review, make sure that you have:
- [ ] Added a solid test coverage and/or screenshots from doing manual
testing
- [X] Done a self-review taking into account security and performance
aspects
- [ ] Aligned any UI changes with the [UI
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)

Release Notes:

- JetBrains macOS bindings: added the missing `ctrl-shift-g` binding for
`editor::UndoSelection`

Change summary

assets/keymaps/macos/jetbrains.json | 1 +
1 file changed, 1 insertion(+)

Detailed changes

assets/keymaps/macos/jetbrains.json 🔗

@@ -33,6 +33,7 @@
       "cmd-+": "editor::UnfoldLines",
       "alt-shift-g": "editor::SplitSelectionIntoLines",
       "ctrl-g": ["editor::SelectNext", { "replace_newest": false }],
+      "ctrl-shift-g": "editor::UndoSelection",
       "ctrl-cmd-g": ["editor::SelectPrevious", { "replace_newest": false }],
       "cmd-/": ["editor::ToggleComments", { "advance_downwards": true }],
       "alt-up": "editor::SelectLargerSyntaxNode",