Bluetooth: Add hci_vs_sdc.h which expose wrappers VS HCI commands

The SDC provides vendor specific Bluetooth functionality through
vendor specific HCI commands.
The APIs added in this commit handles:
 - Building the VS HCI commands
 - Sending the VS HCI command to the controller.
   This works both when the controller is on the same core,
   or if the controller is separated from the host by
   another HCI layer.
 - Return parameters

This removes the need for boilerplate code in applications.

Some of the vendor specific APIs take in handles.
Those can be obtained from host types using the APIs defined
in `zephyr/bluetooth/hci.h`.

The API documentation is referring to the HCI command documentation
to avoid duplication.

Signed-off-by: Rubin Gerritsen <[email protected]>