Add ability to disable resizing of the window

[Gbr22]

It is currently not possible to disable window resizing in gpui-component.

It would be nice if gpui-component inherited is_resizable from WindowOptions, but AFAIK, there is no way to access that value of the window after window creation, so I added the resizable option to Root (and WindowBorder) instead, with true as the default value to maintain the current behavior when unset.

If you are unhappy with the API in the PR, but agree that resizing should be something that can be disabled, then treat this as a feature request.

[huacnlee]

I checked the GPUI window, and it doesn't seem to have anything related to it.

However, your current modification still doesn't work; it only addresses the Linux limitation.

I think this requirement should be addressed by adding this parameter to the GPUI side.