floss: Add GetSupportedRoles API

Add new API GetSupportedRoles that returns a list of BtAdapterRoles,
which can be Central, Peripheral, and CentralPeripheral. This
is based off of controller_shim's get_ble_supported_states() which
returns the LE states from HCI LE Read Supported States command
(Core 5.3, Vol 4, Part E, 7.8.27).

Bug: 310995348
Tag: #floss
Test: manual calling API on brya
Test: mmm packages/modules/Bluetooth
Flag: EXEMPT, floss change for ChromeOS only.
Change-Id: I5a07cee7a3c5c597edd58816d7778d52141eac0d