NativeWindow: implement functions expected by AIDL

ANativeWindow is now parcelable over stable interfaces by being
wrapped in NativeWindow or Surface. The readFromParcel and
writeToParcel functions are implemented for this class, but
AIDL also expects some comparators and a toString function
to be implemented for custom parcelables.

This CL implements the comparison operators, and the toString
function to allow NativeWindow/Surface to be used with AIDL
interfaces and Parcelables. The operations simply
compare/print the ANativeWindow pointer that is being managed
by the object.

Bug: 283283111
Test: Verified that Surface can be used in an AIDL file.
Change-Id: I28ceded9ee1358884a6b1214269bb04a90749fc0