markdown: Add support for inline HTML img tags inside text (zed-industries#37264)

Follow-up: zed-industries#36700

This PR adds basic support for showing images inline inside a text.

As you can see inside the before screenshot, the image was displayed
right below the `Some inline text` text. This was because we didn't
consider the image to be inline with the text (paragraph). Now we do :)

All the test changes are making sure it is not more than 1 element
parsed, instead of only checking for the first parsed element. This
could work out bad when we return more than 1 result.

**Before**
<img width="1717" height="1344" alt="Screenshot 2025-08-31 at 13 49 45"
src="https://github.com/user-attachments/assets/13c5f9dd-0e0a-4e08-b2a6-28e9a4e0cab8"
/>

**After**
<img width="1719" height="1343" alt="Screenshot 2025-08-31 at 13 42 14"
src="https://github.com/user-attachments/assets/bf7aa82f-3743-4fb3-87aa-4a97a550c4d1"
/>


**Code example**:
```markdown
<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)
```

Release Notes:

- Markdown: Added support for inline HTML `img` tags inside paragraphs

Author: RemcoSmitsDev

crates/markdown_preview/src/markdown_elements.rs

@@ -155,7 +155,7 @@ pub struct ParsedMarkdownText {
     /// Where the text is located in the source Markdown document.
     pub source_range: Range<usize>,
     /// The text content stripped of any formatting symbols.
-    pub contents: String,
+    pub contents: SharedString,
     /// The list of highlights contained in the Markdown document.
     pub highlights: Vec<(Range<usize>, MarkdownHighlight)>,
     /// The regions of the various ranges in the Markdown document.