GraphicsBuffer: comparison operators

All AIDL structures are comparable. It makes it possible to use them as keys in a map. We can define an order for any type on the computer, since we can always take the address. Though - this may not always be the most useful meaning.

We didn't discover this earlier, because this was only ever used in an argument. Regardless, it seems like a useful thing to have.

Also - we shouldn't add complexity to AIDL to make this optional. It has deep consequences, since any element, even 4-5 structures deep could cause a struct to not be comparable. If someone adds a non-comparable type to a structure in a later version, AIDL packages depending on it might find it impossible to upgrade without making their structures non-comparable, which could break client code.

Bug: N/A
Test: N/A
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:2d4660083c7eb0ea56040745830abcb148d8de54)
Merged-In: I627adbd110d037246ce307f4984739008fe91c33
Change-Id: I627adbd110d037246ce307f4984739008fe91c33