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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[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 (https://github.com/SAP/ui5-typescript/issues/427) ?