Support aconfig dump --dedup

Add a flag to aconfig dump that will allow identical flags to be merged
without erroring.  This will allow merging the aconfig cache files from
dependencies for each module, which requires passing less data to Make
from Soong, and thus reduces the percentage of builds require Kati
analysis.

Bug: 313698230
Test: aconfig.test
Change-Id: Id2d9b78225720ce01defad4b13ea9395f6ab1033