Apply hint.background and predictive.background colors from the theme

[maxdeviant]

This PR updates the editor to respect the hint.background and predictive.background colors from the theme.

Before	After

Closes #17392.

Release Notes:

• Updated the editor to respect the hint.background and predictive.background colors from the theme.

[zed-industries-bot]

	Messages
📖	This PR includes links to the following GitHub Issues: #17392 If this PR aims to close an issue, please include a Closes #ISSUE line at the top of the PR body.

Generated by 🚫 dangerJS against 029d42b

[maxdeviant]

I'm not sure we want to actually proceed with this.

There are a lot of themes—both built-in and in the extension store—that set the background colors, and I think the end result looks quite bad as-is.

[AlbertMarashi]

@maxdeviant in regards to the built-in themes, we have two options

1. Go through each theme and select a good predictive background highlight (happy to do this)
2. Set all of the colors to #0000 for transparent (this will be effectively a "noop" change)

In regards to extension store themes, unfortunately I think its just a band-aid we have to pull off... Thankfully the fixes/workarounds would be pretty straight forward for both users & theme developers.

In my custom theme, I set any unused colors to #F00 (red) so that I would know to update them if Zed was updated.

[maxdeviant]

@maxdeviant in regards to the built-in themes, we have two options

1. Go through each theme and select a good predictive background highlight (happy to do this)
2. Set all of the colors to #0000 for transparent (this will be effectively a "noop" change)

In regards to extension store themes, unfortunately I think its just a band-aid we have to pull off... Thankfully the fixes/workarounds would be pretty straight forward for both users & theme developers.

In my custom theme, I set any unused colors to #F00 (red) so that I would know to update them if Zed was updated.

An issue I have is that even with appropriate colors selected, I still think the end result looks bad with the background in place.

[maxdeviant]

I'm moving the inlay hints portion of this to a separate PR that puts the rendering of backgrounds behind a setting (that defaults to false): #18010

I haven't yet assessed the state of the world for inline completions.