TypeScript generics to allow declaring GridItem type

[Haprog]

Description

Currently the TS type declarations use type GridItem = unknown; for the item type in all types/interfaces. It would be great if the types would use generics where the item type could default to GridItem (unknown) but it would be able to be overridden in app code when declaring data providers or renderers for example, so that you don't need to explicitly cast the unknown to something else to be able to use item references with TS.

I think all types that use GridItem (directly or nested) should have generics for setting item type.

e.g.

export type GridDataProviderCallback<T = GridItem> = (
  items: Array<T>,
  size?: number
) => void;

export type GridDataProviderParams<T = GridItem> = {
  page: number;
  pageSize: number;
  filters: Array<GridFilter>;
  sortOrders: Array<GridSorter>;
  parentItem?: T;
};

export type GridDataProvider<T = GridItem> = (
  params: GridDataProviderParams<T>,
  callback: GridDataProviderCallback<T>
) => void;

Expected code for accessing props on custom item type

const dataProvider: GridDataProvider<MyItem> = (params, callback) => {
  const foo = params.parentItem.myItemProp;
  // ...
};

Actually needed code for accessing props on custom item type

const dataProvider: GridDataProvider = (params, callback) => {
  const foo = (params.parentItem as MyItem).myItemProp;
  // ...
};

[Haprog]

Also related #2071