Insert at Cursor Brick doesn't work on canvas-based editors (e.g., Google Docs)

[twschiller]

Describe the bug

• https://pixiebrix.slack.com/archives/C0436P48QHY/p1712950068640099

To Reproduce

Steps to reproduce the behavior:

1. Open a google doc
2. Open the snippet manager sidebar
3. Click insert at cursor

Discussion

• In general, our snippet shortcut menu and insert at cursor will have problems on Google Docs because it's a canvas-based editor. Adding support would likely require a research spike
• Some discussion from an OSS library: https://github.com/Amaimersion/google-docs-utils/issues/10