Fix check for Cmd+Click on MacOS for Trees

[colin-grant-work]

What it does

Fixes #10876 by ensuring that on MacOS, we check for meta and not ctrl when handling clicks in the tree widget.

How to test

1. On MacOS
2. Open the navigator
3. Select a node
4. Cmd+click on another node
5. Observe that the second node is selected and the first remains selected.
6. Ctrl+click on a third node
7. Observe that the third node is selected, the first two nodes are not selected, and the context menu is displayed with a rename option.

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[vince-fugnitto]

The changes look good to me 👍

I confirmed that:

• cmd + click works well on macOS - allows multiple selections
• ctrl + click works well on macOS - any previous selection is reset
• ctrl + click works well on Linux - allows multiple selections

[vince-fugnitto]

Ternary looks better ;)