Sheet selector has too much whitespace when there is a large disparity in sheet size

[simonwo]

Workbooks with a big disparity between sizes of sheet push the "Submit" button far down the page. All the whitespace makes this look glitchy.

We do this because we are trying to stop the rest of the page from moving when the user makes a sheet selection, as reducing page motion is important for accessibility. So ideally the rest of the page will continue to be rendered in the same position regardless of which sheet is selected.

What we need to investigate is:

• can we reduce a large disparity in more cases - we set some min/max column widths and in the shown case this is responsible for making one of the sheets very large (notably, it's not a data sheet but a summary sheet) so we might be able to reduce the disparity by wrapping less
• can we make the space look less "blank" and continue to lead the user down the page for sheets with a large disparity (we can't assume that we will "solve" large differences in size because a sheet may contain a cell with large numbers of newlines, which we need to render faithfully)
• can we flex the number of displayed rows for "large" sheets in some helpful way (e.g. show 3 rows for this vertically large sheet but the full 10 rows for others). This is probably a render time problem meaning we'd need to do it in Javascript