fix(material/datepicker): add hideHeader

[naaajii]

adds a boolean Input for mat-datepicker to hide header so the users dont have to pass empty component to remove it

fixes #24337

[naaajii]

not exactly sure whats up with lint, it seems to be passing locally.. :thinking:

[mmalerba]

I'm not sure we want to make this change, because it just adds more complexity to our API surface. I understand that passing an empty component might not feel like the nicest solution, but it does make it possible to support your use case within the existing API. In general I see it as: lets add the APIs that make sense for the "official experience" and the custom header is just a catch-all for people that want to go outside of that

[naaajii]

I do agree with you but having an empty component just to hide header just feels off? It's completely up-to you guys, so feel free to close the PR, I'm just a fellow contributor who is still in learning phase! 😄