fix(iconbutton): handle activation click

[vdegenne]

fixes #5532

[vdegenne]

@asyncliz I followed the same idea as <md-text-button>, however to be totally honest I don't know if that's good or not. Requesting your review.

[asyncliz]

The form label activation is used to make <label> work with some wrapped elements like <input>. I think it's fixing the issue as a side effect by forwarding clicks.

Can we try overriding the click method instead? I think it makes more sense to forward the initial click to the delegated element, rather than trigger a host click which re-triggers a button click.

override click() {
  this.buttonElement?.click();
}

If it's more complicated then I'm open to the current approach, but I want to add some documentation to explain what's going on.

[asyncliz]

Update this to capture both the button and anchor element that could be rendered. Both can have clicks forwarded to them.

@query('.icon-button') private readonly buttonElement!: HTMLElement | null;

[vdegenne]

@asyncliz following #5843