introduce valueType setting for properties to support @type annotation

[devtomtom]

The runtime metadata is currently limited to basic types like int, object, any. For example, with Date-based controls, using any in TypeScript is not ideal. Typically, the preferred types are UI5Date or the native Date.

To address this, introducing the valueType property and use it for displaying in the API Reference.

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[codeworrior]

I'm not happy with the name valueType. The old type also is a type of the property's value. It's just a broader, less limiting type.

The new type is more specific, it's the semantic type whereas type is the type that ManagedObject can handle.

[Thodd]

formalType (as opposed to "actual" runtime type?)
or
apiType since it's the APIs signature?

[devtomtom]

Not needed because we tend to redefine the type property with the content of the @type tag.

[BenReim]

@devtomtom Would this be a solution that applies for the interface generator as well (#427) ?