fix(material/chips): add support for aria-description

[zarend]

Add support for aria-description on mat-chip, mat-chip-option and mat-chip-row. mat-chip-option and mat-chip-row put aria-desciprtion on the same element that already has the aria-label.

aria-description is needed for when developers need to provide more information that in the aria-label. This is especially needed for chip-row when [editable]="true". That's because it gives a way to communicate to screen reader users how to begin editing a chip.