Make the styling of disabled checkboxes more in-line with other disabled form elements and fields

[1312rene]

QCheckboxes really stand out from the other fields if they are disabled, being much darker (or brighter, in dark mode) compared to other disabled elements. Furthermore, applying the native disabled property DOES cause correct styling, but doesn't disable the component properly.

I am not sure if this is intentional, and what is the motivation. I am not sure if the fact that QCheckbox isn't wrapped in a QField like QSelect or QInput make any difference, but if so: it should be a very common form usecase where QField elements are mixed with non-wrapped elements like QCheckbox and RadioButton.

Can you please consider applying styling on the QCheckbox label?