linux: Make prompt detail selectable

[0xtimsb]

Closes #21305

As Linux doesn’t have native prompts, Zed uses a custom GPU-based prompt, like the "About Zed" prompt. Currently, the detail in the prompt isn’t selectable.

This PR fixes that by using the editor's multi-line selectable functionality to make the detail selectable (and thus copyable). It achieves this by disabling editing and setting the cursor to transparent. The editor also does all the heavy lifting, like double-clicking to select a word or triple-clicking to select a line, like what user expects from selectable.

Before/After:

When detail is None or empty string:

Release Notes:

• N/A

[0xtimsb]

@mikayla-maki Thank you! Updated it with Markdown. Above GIFs too.

[mikayla-maki]

Can you rebase on main? #21497 is causing your CI to fail :)

[mikayla-maki]

Thank you!