fix(material-experimental/form-field): add setLabelRequired adapter

[asyncLiz]

No description provided.

[jelbourn]

LGTM

Feel free to ping me when the corresponding change lands in Google so I can merge this.

[jelbourn]

Actually it looks like CI is failing here- is there a new MDC version necessary with the change?

[asyncLiz]

Yes. Once the CL is submitted, we'll need to update this PR with the updated canary build

[crisbeto]

Looks like the MDC change made it into a Canary build and got picked up by the cronjob. https://circleci.com/gh/angular/components/139322

[asyncLiz]

Working on updating this now!

[devversion]

Is the plan that we clean this up as a follow-up? I don't think we'll use that given that we support custom form field controls and/or their associated ng control.

[asyncLiz]

I think it's optional to clean up.

I didn't do a deep dive into the component, but it looks like the <span class="mat-mdc-form-field-required-marker"> accomplishes the same goal.

Instead of doing it in markup, you could do it in this method:

setLabelRequired(isRequired: boolean) {
  if (!this.hideRequiredMarker && this._control.required && !this.control.disabled) {
    // toggles the `mdc-floating-label--required` class
    this._floatingLabel.required = isRequired;
  }
}

Definitely a lot of opinions and unknowns on my part. Feel free to update the comment and either implement something, or leave it as no-op.

[devversion]

Makes sense. I don't think we'll be able to rely on that method since we want to update whenever the input is refreshed, so we rely on change detection. Doing that manually might be overly complicated

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