markdown: Add support for HTML styling attributes

[RemcoSmitsDev]

Second take on #37765.

This PR adds support for styling elements (b, strong, em, i, ins, del), but also allow you to show the styling text inline with the current text.
This is done by appending all the up-following text into one text chunk and merge the highlights from both of them into the already existing chunk. If there does not exist a text chunk, we will create one and the next iteration we will use that one to store all the information on.

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><a href="https://example.com">Link Text</a></p>

<p style="text-decoration: underline;">text styled from style attribute</p>

cc @bennetbo

TODO

• add tests for styling nested text that should result in one merge

Release Notes:

• Markdown Preview: Added support for HTML styling elements

[RemcoSmitsDev]

@bennetbo It looks like CI uses a stale version of the cache, that's why it's failing. Could you clear the cache and restart it?
The PR should be fine after it, and ready for your review.

[bennetbo]

I think the CI failure is expected, since the code is broken after merging main

[RemcoSmitsDev]

I thought I was already update to date, will fix it then.

edit: Ahh the caption PR got merged. Got it now.

[RemcoSmitsDev]

@bennetbo Fixed your review comments.

[bennetbo]

Nice work!