TextEdit demo expands horizontally with no way to shrink

[jh05013]

Describe the bug
The TextEdit demo can expand horizontally by growing the "Selected text", but cannot be shrunk, except by using Reset egui or similar buttons.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://www.egui.rs/
2. Open the TextEdit demo
3. Type and drag a long text

Expected behavior
"Selected text" should be cut (and perhaps use horizontal scroll instead), or the window should shrink back when the text is deselected.

Screenshots

Desktop (please complete the following information):

• OS: Linux Mint
• Browser: Firefox

Additional context

[lucasmerlin]

This is the problem as #5138, so I think we can close this as a duplicate.