fix(material-experimental/mdc-chips): support custom errorStateMatcher

[vanessanschmitt]

MatChipGrid should have an errorStateMatcher Input in order to be
backwards compatible with the old non-mdc MatChipList.

[mmalerba]

Is this just a no-op because only the mat-chip-listbox should actually be used with an input? If that's the case then maybe we shouldn't add this back. We'll just document it as a breaking change to be aware of and recommend that people use the listbox version with inputs.

[vanessanschmitt]

mat-chip-grid is the one that gets used with matChipInputFor. So I think we still want it! There's a use case in Pantheon that I'm trying to migrate to mat-chip-grid where someone is using their own errorStateMatcher.

[mmalerba]

But don't we need to do something with ErrorStateMatcher, it looks like in this PR we're just taking it as an input and then ignoring it. (Unless it just needs to be here for some other component to read it, form-field maybe? It's been a while so I can't really remember how it's all hooked up 😄)

[vanessanschmitt]

Oh haha I see what you're saying! It does look like that. I think it's being used here in mixinErrorState: https://github.com/angular/components/blob/master/src/material/core/common-behaviors/error-state.ts#L55 which is part of _MatChipGridMixinBase
here: https://github.com/angular/components/blob/master/src/material-experimental/mdc-chips/chip-grid.ts#L73

[mmalerba]

Ahh ok, figured it was just me being dumb

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