Please show mxc URL when zooming (click-select) images

**Is your suggestion related to a problem? Please describe.**
There are a few places require mxc:// url-s, from `myroomavatar` to inline images. Can't find it easily.

**Describe the solution you'd like**
Every click-displayed (zoomed in) image may get a caption of mxc url.

**Describe alternatives you've considered**
View image URL, cut and fabricate mxc, murmur impolite words.

Some people are using bots to display it, but it will only work for messages, not avatars and like.

Start by locating the image zoom or click-display entry points in the Element clients, including the avatar and inline-image cases mentioned in the issue. Check how the displayed image URL is currently exposed; done means every zoomed image provides a caption containing its mxc:// URL, including images and avatars outside messages.

Written by the indexing model from the issue text.