gpui: Implement inline box text layout

[MatinAniss]

This is an implementation of inline boxes in text layouts, this allows you to have spaces at certain points of your text layout where you can have "inline elements" in these spaces that flow with your text layout.

The gpui text system should look into moving to Parley in the future, which already supports text layouting features such as inline text boxes. Moving to Parley would require some much larger changes but will be better in the long run.

Closes #10916

Current State:

• The text line still needs to adjust its line height if a inline box height exceeds it, but this isn't a must need.

text-inline.mp4

Release Notes:

• N/A

[huacnlee]

Why not use span, Span::new, like the before div.

And the next add_text, add_element.

I think we can try to have a better API like this if it's possible:

div().id("paragraph")
  .child(span("This is an inline element ->"))
  .child(span().w_4().bg(gpui::red()))
  .child(span("text"))

Or at least we can:

div().id("paragraph")
  .child(
    InlineText::new()
      .child("This is an inline element ->")
      .child(div().w_4().bg(gpui::red()))
      .child("text")
  )

[mikayla-maki]

This is a good idea, and one we really want to have in Zed. However, I'm not convinced on the API yet, I'd think this would be a display mode on the div, right?

I've let this one languish, so I'm going to close it for now.

[MatinAniss]

Agreed, I wasn't too confident on my implementation and It would be better to utilise Parley instead but that requires some larger changes that I haven't had the time to look into deeply.