gpui: Add interval in pattern (#26459)

Closes #ISSUE

[git: Use font size to determine pattern slash width
#26446](https://github.com/zed-industries/zed/pull/26446)

This PR only uses font size as the slant line width, and here it further
uses line height as the slant line interval control.

before


![image](https://github.com/user-attachments/assets/a8f2406e-5eed-4528-a9a2-867513613fc7)


now


![image](https://github.com/user-attachments/assets/9b8ccca9-8023-4cb2-a6fe-0e42e19642a4)

big line height


![image](https://github.com/user-attachments/assets/4498e858-4f25-432c-80ee-355726d9c41b)


Release Notes:

- N/A *or* Added/Fixed/Improved ...