Move DiffWrapperBase into a seperate utility class.

This enables us to use abi-diffing both while doing an abi diff between
two libraries and also while comparing two records / enums for an ODR
violation.

Bug: 71486971

Test: make -j64

Change-Id: Ic778b9fe8824835b7380ad1740751d8d4bcca9d6
5 files changed