MdeModulePkg ConSplitterDxe: Support toggle state sync

MdeModulePkg ConSplitterDxe: Support toggle state sync

Register key notify for toggle state (CapsLock, NumLock and ScrollLock)
sync between multiple keyboards.
The implementation for this feature requires keyboard driver supports
EFI_KEY_STATE_EXPOSED, and turns on physical TextInEx partial key
report for toggle state sync.
The virtual TextInEx will report the partial key after it is required
by calling SetState(X | KEY_STATE_VALID_EXPOSED) explicitly.

Cc: Ruiyu Ni <Ruiyu.ni@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Cc: Feng Tian <feng.tian@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Ruiyu Ni <Ruiyu.ni@intel.com>