shared/gatt-server: Implement "Read By Type" request.
shared/gatt-server: Implement "Read By Type" request.

This patch implements the ATT protocol "Read By Type" request for
shared/gatt-server. Logic is implemented that allows asynchronous
reading of non-standard attribute values via the registered read and
read completion callbacks.

silent-snowman/bluez,pstglia/external-bluetooth-bluez,pstglia/external-bluetooth-bluez,ComputeCycles/bluez,ComputeCycles/bluez,pkarasev3/bluez,pstglia/external-bluetooth-bluez,silent-snowman/bluez,silent-snowman/bluez,mapfau/bluez,pkarasev3/bluez,silent-snowman/bluez,pstglia/external-bluetooth-bluez,pkarasev3/bluez,mapfau/bluez,mapfau/bluez,ComputeCycles/bluez,pkarasev3/bluez,mapfau/bluez,ComputeCycles/bluez