use formDisabledCallback to support <fieldset> disabled attribute

What is affected?

Component

Description

See: https://jsfiddle.net/datvm/zdpeqc5j/1/

For standard components, when an acestor <fieldset> has [disabled=true], they are disabled as well. I think this behavior is not discussed yet so it's probably not a bug? Would you consider adding this feature?

Note: the screenshot above misses <md-select>.

Reproduction

https://jsfiddle.net/datvm/zdpeqc5j/1/

<fieldset disabled>
    <p>
        <md-filled-button>A Material 3 Button</md-filled-button>
        <button>Standard button</button>
    </p>
    
    <p>
        <md-outlined-text-field></md-outlined-text-field>
        <input value="Standard input" />
    </p>
    
    <p>
        <md-checkbox></md-checkbox>
        <md-switch></md-switch>
        <input type="checkbox" value="Standard input" />
    </p>
    
    <p>
        <md-radio></md-radio>
        <input type="radio" value="Standard input" />
    </p>
    
    <p>
        <md-slider></md-slider>
        <input type="range" />
    </p>
    
</fieldset>

Workaround

You have to manually set disabled to each component in the fieldset.

Is this a regression?

No or unsure. This never worked, or I haven't tried before.

Affected versions

1.0.0

Browser/OS/Node environment