refactor(mdc-chips): Make MatChipTextControl publically available. (#16820)

Make the MatChipTextControl class available for implementation by other classes, so input fields other than <input> elements - eg. custom <div>s - can be used with mat-chip-grid (which currently assumes a matChipInputFor <input> is provided).

(cherry picked from commit 2baa362)

Author: kor-k

src/material-experimental/mdc-chips/public-api.ts

@@ -16,3 +16,4 @@ export * from './module';
 export * from './chip-input';
 export * from './chip-default-options';
 export * from './chip-icons';
+export * from './chip-text-control';