dart:ffi hide or restrict Pointer.address and fromAddress

[dcharkes]

Do you have a pressing need for pointer<->integer conversion? Even in C++ that is usually only necessary in ultra low-level code (e.g. kernel drivers) and otherwise invites risky trickery (e.g. some struct offset arithmetic magic that gets brittle).

I'd leave that part out, or restrict it's use.

Especially if the dart:ffi library calculates sizes and field offsets itself, wrapper writers probably often do not want to expose the integer addresses to the users.

How can we enable wrapper writers to disallow wrapper users to use fromAddress and .address?

Related to: #35841