gpui: Align SVG sprites to whole pixels (#15822)

Related to https://github.com/zed-industries/zed/issues/12352 (and old
issue https://github.com/zed-industries/zed/issues/643)

This fixes visual glitches that could happen when rendering icons on
Linux and Windows (and in the Blade backend)


![image](https://github.com/user-attachments/assets/02646d1d-d35b-48be-89c9-189416510cf2)

![image](https://github.com/user-attachments/assets/ccf99867-25d2-40fb-8735-c540f8cf793a)

![image](https://github.com/user-attachments/assets/8d1124a3-669e-4be5-8b46-5dc2df14a28a)


Release Notes:

- Linux: Fixed visual glitches when rendering icons.