Add option to turn off "hit ALT for prediction" popup

[danfuzz]

When in "subtle" edit prediction mode, Zed seems to like to overlay a little hint that reminds one that they can press ALT to get a prediction:

I see the utility in adding a prediction preview when there are other possible completions (that is, from the language server), but, speaking personally, this little giblet by itself is annoying and distracting, and I'd love to have a setting to turn it off without turning off edit predictions entirely.

[remorses]

An alternative would be to use a different color the cursor, for example make it red when there is a prediction available

[claudio4]

I’d really love to have this feature.

I want to be able to test and access AI suggestions when I need them, but when I’m not interacting with them, I’d prefer they stay unobtrusive and not distract me while I work.

[matt-h]

Agree, I use the AI completions rarely, it seems like a waste to always be looking for predictions and popping up with the annoying popup here.

Ideally, I want it off but will then look for predictions when I press the key.

[dlight]

I think it should be tristate, yeah. One for displaying predictions, another for subtly displaying whether a prediction is available (not this popup: I liked the idea of another cursor color), and another that doesn't display anything. It should be in the same place where "diagnostics" and "inline diagnostics" is defined, in the "edit controls" button.

What can be done now is to entirely disable predictions, but then holding alt to show them doesn't work. Indeed I think that with this change, the edit predictions toggle becomes redundant (if nothing is displayed until you hold alt, then just don't press alt for disabling predictions)

[dlight]

Also, note that this goes in the same direction as disabling squiggly lines as in #20871, to declutter the experience (but granted, it's already possible to disable edit predictions, it's just not possible to selectively enable it with a key without this pop up showing)