MdeModulePkg/VariableFlashInfoLib: Add initial library

MdeModulePkg/VariableFlashInfoLib: Add initial library

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=3479

Adds a new library class VariableFlashInfoLib that abstracts access
to variable flash information. The instance provided first attempts
to retrieve information from the Variable Flash Info HOB. If that
HOB is not present, it falls back to the PCDs defined in
MdeModulePkg.

This fall back behavior provides backward compatibility for platforms
that only provide PCDs but also allows platforms that need to
dynamically provide the information using the Variable Flash Info HOB
to do so at runtime.

Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Hao A Wu <hao.a.wu@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>