Add support for remote images in hover popups

[jwortmann]

Fixes #1363.

I have tested it with a small modification to LSP-pyright:

--- Installed Packages/LSP-pyright/plugin.py
+++ Packages/LSP-pyright/plugin.py
@@ -94,6 +94,7 @@
             contents = hover.get("contents")
             if isinstance(contents, dict) and contents.get("kind") == "markdown":
                 contents["value"] = self.patch_markdown_content(contents["value"])
+                contents["value"] += "\n\n![](https://flutter.github.io/assets-for-api-docs/assets/material/Colors.pinkAccent.png)"
             return
         if method == "completionItem/resolve" and isinstance(response.result, dict):
             completion = cast(CompletionItem, response.result)

The following is mentioned in the mdpopups docs, but it has been published more than two years ago, so I guess it's fine to add now:

[rchl]

It looks like this could trigger an issue like:

• the popup is shown
• images start resolving
• the original popup is closed and a different one is opened
• the original resolve completes and replaces the new popup with original contents.

Should we have some safety measures to ignore resolved results that are "outdated"?

[jwortmann]

Probably needs a larger refactoring for tracking popups then, see also

LSP/plugin/documents.py

Lines 575 to 577 in e7cd48f

	# TODO: Refactor popup usage to a common class. We now have sigHelp, completionDocs, hover, and diags
	# all using a popup. Most of these systems assume they have exclusive access to a popup, while in
	# reality there is only one popup per view.

But since there seems to be image caching and a size cap implemented in mdpopups, I wonder how realistic such a situation would be. I would say self.view.is_popup_visible() should be an adequate solution for now.

[rchl]

I don't know if this code will ever trigger in my usage of LSP but I imagine that if someone deals with servers or content where this would trigger then it could suddenly become a fairly easy to trigger issue.

But I'm fine with not addressing it for now.

[jwortmann]

Here is a simple way to test it with Pyright:

def show_cat():
    """ Cute cat photo on hover.
    
    ![](https://upload.wikimedia.org/wikipedia/commons/8/8e/Hauskatze_langhaar.jpg)
    """
    pass

I guess it depends on your internet connection speed, but on my end the delay is negligible, in the way that I doubt you can open another popup in the meanwhile. The image size is ~1MB.