Fix terminal line background being reset on each line (#7040)

Release Notes:

- Fixed #5027
- Fixed #5079

Info:

The terminal draws a rectangle for the background color of cells, but
this was being reset on every line. The effect of this was that tools
like Vim, Helix, and git-delta would only have one line with a
background color:

<img width="979" alt="Screenshot 2024-01-30 at 2 48 13 pm"
src="https://github.com/zed-industries/zed/assets/52195359/ab1873d2-0653-44c6-9406-bc2a277d9a2f">

After this change:

<img width="1011" alt="Screenshot 2024-01-30 at 2 49 45 pm"
src="https://github.com/zed-industries/zed/assets/52195359/6e4d2a70-590b-48b0-a464-4c827f55622e">
b865db455dRobert Clover committed on 1/30/2024, 5:01:02 AM· committed by GitHubparent372bc42
1 file changedLine totals unavailable