[foreign] proposal - addressOf

[Maurizio Cimadamore]

Hi,
in light of feedback from [1] and [2], I'd like to propose that all C 
carriers:

Pointer
Array
Struct
Callback

provide an 'addressOf' method which returns a Pointer to X, where X is 
the original carrier. This would also mean renaming the current 
Struct::ptr to Struct::addressOf. Good? Bad?

[1] - 
https://mail.openjdk.java.net/pipermail/panama-dev/2019-February/004319.html

[2] - 
https://mail.openjdk.java.net/pipermail/panama-dev/2019-February/004626.html