refactor: move state management out of DaprClientImpl (#1902)

Move getState, getBulkState, saveBulkState, deleteState,
executeStateTransaction, queryState and their proto mapping into a
package-private DaprStateClient class. The public methods on
DaprClientImpl keep their signatures and delegate to it.
No public API change.

Part of #1875

Signed-off-by: Javier Aliaga <javier@diagrid.io>
Signed-off-by: artur-ciocanu <artur.ciocanu@gmail.com>
Co-authored-by: artur-ciocanu <artur.ciocanu@gmail.com>

Author: javier-aliaga