MdeModulePkg/HiiDB: Share default if some default value are not specified

MdeModulePkg/HiiDB: Share default if some default value are not specified

Add a new implementation policy of getting default value in HiiDatabase.
The new policy is only for the situation that a question has default
value but doesn't have default value for all supported default type.
In this case, we will choose the smallest default id from the existing
defaults, and share its value to other default id which has no
default value.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>