markdown: Add support for HTML styling elements

[RemcoSmitsDev]

Follow-up: #37264

This PR adds support for all the common HTML styling elements (b, strong, em, i, ins, del).
It also fixes an issue where we would insert an extra paragraph for new line text that resulted in adding a new line inside the markdown.

Before

After

Code example:

<p>some text <b>bold text</b></p>
<p>some text <strong>strong text</strong></p>
<p>some text <i>italic text</i></p>
<p>some text <em>emphasized text</em></p>
<p>some text <del>delete text</del></p>
<p>some text <ins>insert text</ins></p>

<p>Some text <strong>strong text</strong> more text <b>bold text</b> more text <i>italic text</i> more text <em>emphasized text</em> more text <del>deleted text</del> more text <ins>inserted text</ins></p>

<p>some inline text <img src="https://picsum.photos/200/300" alt="Description of image" style="height: 100px" /> asdjkflsadjfl</p>

# Html Tag
<img src="https://picsum.photos/200/300" alt="Description of image" />

# Html Tag with width and height
<img src="https://picsum.photos/200/300" alt="Description of image" width="100" height="200" />

# Html Tag with style attribute with width and height
<img src="https://picsum.photos/200/300" alt="Description of image" style="width: 100px; height: 200px" />

# Normal Tag
![alt text](https://picsum.photos/200/300)

cc @SomeoneToIgnore

Release Notes:

• Markdown: Added support for HTML styling elements

[SomeoneToIgnore]

I'm quite out of the context here, and decided to check on how images are rendered.

It also fixes an issue where we would insert an extra paragraph for new line text that resulted in adding a new line inside the markdown.

1. Here, it seems that all the padding (?) around the images and items is gone.

https://github.com/rust-lang/rust-analyzer/blob/master/docs/book/src/contributing/debugging.md

Current Zed shows it a bit better?

2. Here, there's a large spacing between images compared to what GH renders:

https://github.com/rust-lang/rust-analyzer/blob/master/docs/book/src/contributing/guide.md

Current Zed seems to do the same.

3. As very well noted in #37264 (comment) seems like there's a regression:

Should we, instead of piling more changes, fix this trash first?
This got reverted in #37893, but overall was right, it seems, so if we get this back, let's ensure Zed's markdowns are rendered normally.

1. and 2. would be nice to improve too, but this is was a straight regression.

[Angelk90]

@RemcoSmitsDev :

You can also adjust the style of the tag usage `

Add some side padding, and rounding, see table images.

Code:

We use [`cargo-about`](https://github.com/EmbarkStudios/cargo-about) to 

Github	Vscode	Zed

[RemcoSmitsDev]

@Angelk90 i think that is more a ui/ux issue. This pr just adds basic support for styling attributes. We can extend this in the future with more css properties. So its a bit out of scope for what i wanted to add/fix

[Angelk90]

@RemcoSmitsDev : I understand, you might consider fixing it in the future.
I don't like seeing it like this.

[RemcoSmitsDev]

Yeah for sure!

[RemcoSmitsDev]

This PR is depending/waiting on inline elements support, to correctly show all the cases you could use style tags.
Right now, added style tag inside a p tag, will break the text inside it to the next line because the element is a block element, as we disabled the flex & flex wrap.

See screenshot impl without showing the style tags inline with the flex & flex-wrap

@SomeoneToIgnore Do you have time to brainstorm about how we could support inline elements. I already did some digging in how we could support this, and I tried to implement this inside taffy, but it seems there is a limitation because you can't wrap a part of the text to parent block start position if it's inline displayed.

See current impl for inline support with taffy

Screen.Recording.2025-09-20.at.17.09.07.mov

[SomeoneToIgnore]

Sorry, I have no good clues on this and improving markdown rendering is not in any of the company's intermediate plans: from my side, I'm mainly concentrating on rainbow brackets, LSP features like inlays/semantic highlights and community work (PR reviews alone is huge).

I'm happy to help to do a basic review and testing, but not sure can handle anything more intelligent on top.

[SomeoneToIgnore]

I've actually agreed with @bennetbo to get the related PRs over to him, as he has definitely more context than me on what's going on and could suggest something (❤️ )

[bennetbo]

Sorry for taking so long to review. I'll close this for now as there are conflicts. If you'd like to fix the conflicts & re-open I'm happy to review (Feel free to ping me, and I'll make sure to review it quickly)

[RemcoSmitsDev]

Happy to fix the conflicts but don't think the PR good enough to merge as it does not support showing the text inline for these HTML elements. I have an idea how we could get around it, will try that out soon, but need's some refactoring I think.