Previously, the snapshot code did not know whether a specific property
could be arch specific or not and assumed that they all were which
meant that it could generate snapshots containing arch specific values
for properties that are not arch specific and so would fail when
unpacked.
This change requires arch specific fields in SdkMemberProperties to be
tagged as such using `android:"arch_variant"` (just as in module input
property structures). Any property without that must have properties
that are common across all variants.
Bug: 155628860
Test: m nothing
Change-Id: I3df60f0b53ba02ec2c55a80c7da058eac5909d26
864e1b45db