[bt][bredr] Outgoing connections for profiles

Add fuchsia.bluetooth.bredr.Profile.ConnectL2cap() FIDL API for opening
channels to remote devices for profiles.  This is necessary to
implement any client-side profiles.

Added BrEdrConnectionManager.OpenL2capChannel which manages the translation
between remote device_id and connection handle.

Bug: BT-423
Test: TODO - BT-659

Change-Id: Ic5a91569771505ef9ad522eff2cd0610e67549ee
5 files changed