Render markdown image syntax in documentation. Relative URLs are fetched from the project directory; absolute URLs are hotlinked from wherever they point.
Syntax and URL resolution:
```
# In New_Project27/src/Main.enso
## Main method docs
- Image at `New_Project27/src/image.jpg`: ![Image](image.jpg)
- Image at `New_Project27/image.png`: ![Image](../image.png)
- Image at `New_Project27/src/image.jpg`: ![Image](/src/image.jpg)
- Image at `New_Project27/image.png`: ![Image](/image.png)
main =
42
```
https://github.com/enso-org/enso/assets/1047859/3f873f3f-31b1-44bf-ae3e-2f467f2d546dCloses#10058.
# Important Notes
Stacked on #10064.
#### New documentation panel:
- Shows documentation of currently-entered method.
- Open/close with Ctrl+D or the extended menu.
- Renders markdown; supports WYSIWYG editing.
- Formatting can be added by typing the same markdown special characters that will appear in the source code, e.g.:
- `# Heading`
- `## Subheading`
- `*emphasis*`
- Panel left edge can be dragged to resize similarly to visualization container.
https://github.com/enso-org/enso/assets/1047859/6feb5d23-1525-48f7-933e-c9371312decf
#### Node comments are now markdown:
![image](https://github.com/enso-org/enso/assets/1047859/c5df13fe-0290-4f1d-abb2-b2f42df274d3)
#### Top bar extended menu improvements:
- Now closes after any menu action except +/- buttons, and on defocus/Esc.
- Editor/doc-panel buttons now colored to indicate whether editor/panel is open.
https://github.com/enso-org/enso/assets/1047859/345af322-c1a8-4717-8ffc-a5c919494fedCloses#9786.
# Important Notes
New APIs:
- `DocumentationEditor` component: Lazily-loads and instantiates the implementation component (`MilkdownEditor`).
- `AstDocumentation` component: Connects a `DocumentationEditor` to the documentation of an `Ast` node.
- `ResizeHandles` component: Supports reuse of the resize handles used by the visualization container.
- `graphStore.undoManager`: Facade for the Y.UndoManager in the project store.