For Ivy's template type checker it is possible to let a directive
specify static members to allow a wider type for some input:
```typescript
export class MatSelect {
@Input() disabled: boolean;
static ngAcceptInputType_disabled: boolean | string;
}
```
This allows a binding to the `MatSelect.disabled` input to be of type
boolean or string, whereas the `disabled` property itself is only of
type boolean.
Up until now, any static `ngAcceptInputType_*` property was not
inherited for subclasses of a directive class. This is cumbersome, as
the directive's inputs are inherited, so any acceptance member should as
well. To resolve this limitation, this commit extends the flattening of
directive metadata to include the acceptance members.
Fixes#33830
Resolves FW-1759
PR Close#34296
22ad701134