feat(Table): `onFilter` gets filtered rows

[adamhock]

• onFilter now has an additional parameter filteredData which users can get their filtered rows from.
• onFilter is now called in Table.tsx instead of filterHandler.ts because there's no way to get filtered rows in the state reducer. Because of this, onFilterHandler now only returns the filters.
• previousFilter and currentFilter are used to track when the filters are changed so onFilter is only called when this occurs. These are checked in a .useEffect after the stateReducer runs all the handling.

Closes iTwin/iTwinUI-react#816

[adamhock]

Have you tested with subrows?

subrows have been tested!