Switch icon (#16363)

Updates instances of the `MagicWand` icon to our more recent `Sparkle` /
`ZedAssistant` icon in places where we reference inline assist.

Before:

![CleanShot 2024-08-16 at 13 41
58@2x](https://github.com/user-attachments/assets/67af27a2-a09b-44bb-a8af-2bafcbbd9038)

After:
![CleanShot 2024-08-16 at 13 48
34@2x](https://github.com/user-attachments/assets/229ccc8e-8a93-44c1-abe0-7b6e22ca93e2)


Release Notes:

- Updated inline assist icon in the editor & terminal.