fix: buttons' appearance in disabled fieldset

[datvm]

Fix #5562

[datvm]

One change that is different compared to the others is:

.outlined:disabled .icon
// to
:host(:disabled) .outlined .icon {

Because the button inside the shadow root is not actually disabled. I don't think this should affect anything else.

[datvm]

A second commit also fixes other controls: Checkbox, Radio, Select, Slider and Switch.

Now this standalone commit does not help much as it doesn't fix the issue with #5409 but this commit prepares for when we fix that one. Right now the only way to test it is to put them in a disabled fieldset and then manually set their disabled to false (which means the fieldset is still disabled but each individual component is not).

[asyncLiz]

Thanks for this PR, I agree with your approach! There's a couple changes I'd like to make, so I'm going to import this directly for those to get it landed faster.

No action needed from you! Just don't push any more commits to this PR :)