MdeModulePkg/Library: Add HiiGetStringEx to UefiHiiLib for EDK2 Redfish

MdeModulePkg/Library: Add HiiGetStringEx to UefiHiiLib for EDK2 Redfish

Add HiiGetStringEx and leveraged by HiiGetString function to support
getting string with the best language in optionally. This avoids the
string in x-uefi language is misled to the language defined by
"PlatformLang" or the "Supported Languages". This change is introduced
to support x-uefi keyword language for configuring BIOS setting.

Signed-off-by: Jiaxin Wu <jiaxin.wu@intel.com>
Signed-off-by: Siyuan Fu <siyuan.fu@intel.com>
Signed-off-by: Fan Wang <fan.wang@intel.com>
Signed-off-by: Abner Chang <abner.chang@hpe.com>
Cc: Dandan Bi <dandan.bi@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Nickle Wang <nickle.wang@hpe.com>
Reviewed-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>