Allow widgets to specify minw/minh according to their intrinsic size

[DaveInDev]

As you suggested, following this remark :
Button text will automatically clip to fit within the button's boundary. Adding minw makes sense in this case but, sorry, there currently is no way to force minw to always match the button's intrinsic size. But please feel free to open an issue on GitHub to request this feature.

I write this FR.
What I meant precisely is : having an attribute like "fitatleastinnercontent = true", that would verify that the size of a button will never go under its label size, so that it won't never be cropped, even if it's size is relative (expand = true or w=n%, etc...). Then, it would be preferable to see most right side buttons disappear into the right side of the wondow. Hope I'm clear....