Fix text bounds cutoff in iced_wgpu

[DKolter]

Fixes #2963

The current wgpu text bounds implementation casts the right and bottom bound to an integer without rounding, leading to letters not being displayed fully.

In this example there is a combo box on the left with a 0.2px vertical space and an input box on the right without a vertical space. The default font size is 16px, leading to a default line height of 1.3 * 16px = 20.8px. With a 0.2px vertical space the bottom bound equals to a whole integer coordinate, so the letters are displayed correctly. On the right the bound is cast from 20.8px to 20px, loosing almost a pixel of all letters extending to the bottom line:

This PR matches the line bound calculation of tinyskia and rounds the text bounds:

[hecrj]

Is this fixed by #2768?

[edwloef]

No, however the result is a similar kind of snapping, the only difference being the top left point being truncated instead of rounded. Maybe that could be done here as well, though I can hardly say whether it'll be an issue in this case.

This needs a cryoglyph rectangle, which has signed coordinates (for some reason) so the existing snap fn wasn't used before or now.

[hecrj]

Thanks!