UI5WC Wrapper: use index accessed & `UI5CustomEvent` type.

[Lukas742]

If applicable:

• Use index accessed type for ui5wc props instead of importing the type or defining it ourselves.
• Use ui5wc UI5CustomEvent instead of our Ui5CustomEvent

E.g.:

• https://github.com/SAP/ui5-webcomponents-react/blob/main/packages/main/src/webComponents/Button/index.tsx#L67 -> UI5WCButton['design'] (UI5WCButton => Button class)
• https://github.com/SAP/ui5-webcomponents-react/blob/main/packages/main/src/webComponents/Button/index.tsx#L169 -> (event: UI5CustomEvent<WCButton, 'click'>) => void

[Lukas742]

Sorry, I initially created the issue in the wrong repo... I've moved it now to ui5-webcomponents-react