FR: Cmd + Shift + Plus / Minus to increase/decrease font size consistently

[thiagowfx]

Out-of-the-box, the shortcut to increase/decrease font sizes in Ghostty on macOS is Cmd + + and Cmd + -, respectively (no Shift).

With Shift:

Observed: Cmd + Shift + + inserts a literal '+', and Cmd + Shift + - decreases the font size.

Expected: Cmd + Shift + + should increase the font size as well, consistently.

Why is the behavior for Cmd + Shift + + different? This seems unintentional.

Note that this is the out-of-the-box behavior in both Terminal.app and iTerm2.

[mitchellh]

Approved #3899