[base] Improve API consistency

[michaldudak]

This PR brings consistency to Base UI components and hooks' parameters and return values:

1. Whenever a hook needs a ref, it's now called <slot_name>Ref, which matches the get<slot_name>Props` in the return value.
2. All hooks that accept external refs now return merged refs, so combining multiple hooks on one element is easier. This was proven necessary in several compound components (like menuItem being both a button and a list item). The type of this value is React.RefCallback as using the more general React.Ref caused variance issues.
3. Type of accepted refs was standardized to React.Ref<Element>
4. Naming and typing of the forwarded ref in unstyled components were standardized - it's forwardedRef: React.ForwardedRef<Element> (unless a more specific type is needed).
5. The shape of the definition of unstyled components was standardized - it's React.forwardRef(function Component(props: Props, forwardedRef: React.Ref<Element>) { ... });. Specifically, the generic parameters of forwardRef were removed as they are specified in function arguments.
6. The disabled value was removed from useButton's returned object. It's not calculated inside the button, so it was pointless to have it.
7. All unstyled components now receive the generic props (over RootComponentType).
8. Many generic parameters in unstyled components were given more descriptive names.

[mui-bot]

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[mnajdova]

The changes make sense 👍