Request correct dimensions for image thumbnails

[lukebarnard1]

With dynamic thumbnails enabled:

Before changes:

After changes:

This is for when dynamic thumbnails are enabled on the home server, which will scale to exactly the dimensions provided. Synapse comments allude to clients specifying the correct width and height when requesting thumbnails.

[dbkr]

So, I think it's synapse that's at fault here rather than riot: the bug is matrix-org/synapse#1677

The idea is that the media repo worries about maintaining aspect ratio when scaling the image so the client doesn't have to. The client is only able to do this in this case because the other end has told it what it thinks the dimensions are which is not a terribly reliable mechanism, so the width and height specified by the client are a bounding box rather than exact dimensions. In any case, I would say that synapse's behaviour WRT aspect scaling should be consistent whether or not it has dynamic thumbnailing turned on or not.

[lukebarnard1]

This has been made redundant by matrix-org/synapse#1945