## Context

Previously, markdown images failed to load workspace-absolute paths.
This updates the image resolver to identify the active workspace root
directory. Paths which are workspace absolute are correctly resolved and
rendered. The added test covers a successful resolution.

This PR re-implements the fix that was originally proposed in my
previous PR, #52178.

## Fix


https://github.com/user-attachments/assets/d69644ea-06cc-4638-b4ee-ec9f3abbb1ed

## How to Review

Small PR - focus on two changes in the file
`crates/markdown_preview/src/markdown_preview_view.rs`:
- `fn render_markdown_element()` (lines ~583-590): added the logic to
determine the workspace_directory
- `fn resolve_preview_image()` (lines ~714-726): added
workspace_directory variable, and a verification to create the full path
when a path is workspace-absolute

One test was added, covering a successful resolution
(`resolves_workspace_absolute_preview_images`). This test was
implemented in the file
`crates/markdown_preview/src/markdown_preview_view.rs`.


## Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [ ] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Closes #46924 

Release Notes:

- Added workspace-absolute path detection in markdown files