Add media size selection to confirmation screen.

[pixlwave]

Adding another issue to refine the scope of #4479 to just cover #4721.

Once #4721 has been merged it would be great to have a secondary option to choose the size of an image/video when the "Confirm size when sending" toggle has been disabled, along the lines of some of the designs seen in the original issue:

Originally posted by @niquewoodhouse in #4479 (comment):

After a brief design exploration of the issue we came to some solutions:

• Alter the confirm screen to include file size option

Would give people (harder) access to the option if they needed it, but make the flow easier for most users who don't want to edit size.

We did consider some other ideas, but they expanding the work more than we probably require at this stage.

[pixlwave]

Originally posted by @niquewoodhouse in #4479 (comment):

Just thinking slightly longer-term for this, it might be that we have a low-quality mode that just auto-sends at small file sizes:

Or we have more detailed settings section that includes a low-quality mode option + an always confirm option for people who insist on picking the size themselves.

[rda0]

Please consider that the defaults are to send with a lower resolution. I think some people are unintentionally wasting a lot of their media quota or server disk space.

Element-Android reduces the image size by default.