MdeModulePkg: Allow dynamic generation of HEST ACPI table

Introduce the HEST table generation protocol that allows platforms to
build the table with multiple error source descriptors and install the
table. The protocol provides two interfaces. The first interface allows
for adding multiple error source descriptors into the HEST table. The
second interface can then be used to dynamically install the fully
populated HEST table. This allows multiple drivers and/or libraries to
dynamically register error source descriptors into the HEST table.

Co-authored-by: Thomas Abraham <thomas.abraham@arm.com>
Signed-off-by: Omkar Anand Kulkarni <omkar.kulkarni@arm.com>
Change-Id: I72ce299cc71d487355d5e7795aae9efb318975eb