ART: Add pointer-size template to some reflection functions

The unstarted runtime may run code for a different pointer size,
even when no transaction is active (e.g., during startup). To
retain performance when the runtime is up and executing under
normal conditions, add a template parameter and use sizeof(void*)
in places where it is adequate.

For maintainability, it is necessary to drop the default for
the transaction template parameter. Implicit conversions from
bool to size_t may lead to incorrect code and hard to diagnose
problems. So instead ensure that all callers must give all
template parameter values.

Test: m test-art-host
Change-Id: I3076883422c8553ede4de5642409c5684a5a9aa8