[UR] Add spec and implementation for urQueueGetGraphExp

[mmichel11]

Introduces UR graph spec and implementation for urQueueGetGraphExp which returns graph handles from a recording queue. The following changes are made:

• A map of L0 to UR graph handles is made to fetch UR graph handles from across command lists. This allows UR to fetch the correct graph handle if created by a separate command list manager due to fork-join. Map is stored in the context and protected by a lock.
• Map entries are added and removed in graph creation and destruction respectively.
• In implicit recording mode (where the user makes no urGraphCreateExp call), graph handle creation is done in the first instance of urQueueGetGraphExp (if it occurs) instead of urQueueEndCaptureExp as the user must be returned a ur_exp_graph_handle_t.