AAPT2: Parse an ID encoded as a map

ID types should not be encoded as a map. AAPT and AAPT2 emit
IDs as boolean types.

Some apps exist that for some reason have their ID types encoded
as empty maps. This is the case only for the auto generated IDs
from enum values in <attr> tags.

Allow IDs as maps and ignore their content when processing an APK
for optimizing.

Also fixes an issue with expected size of the ResTable_package struct.

Bug: 35861796
Test: tested against the APK in b/35861796
Change-Id: I29a19cd9777bb10bed6766cd42e35e50e098797b