option_as_meta behaviour should be enabled by default on linux

[jakobhellermann]

As far I can tell, on macOS the option_as_meta makes it so that ⌥p gets translated to \ESC p, which is expected by some CLI programs like Emacs.

The setting is named this way because macOS's Terminal and iTerm have that setting as well.

However, I believe that on Linux (and presumably Windows) this behaviour is not only expected, I'm not sure there's even a case to be made for disabling it.
I ran into this because the fish keybindings alt-p didn't work, and I didn't find this setting until looking at the zed code itself.

I'm not sure if zed supports platform-dependent defaults, but is there any disadvantage to always enabling alt_is_meta on non-macOS platforms?