RFR: Turn ShenandoahHeapRegion::{Size,Shift} into the type-checked getters

[Aleksey Shipilev]

Hi,

We have lots of cases where we downcast ShenandoahHeapRegion::{Size,Shift} to
jint. While this is probably safe in most cases, compilers complain, and don't
let us build. This introduces the type-checked getters, and changes all uses
appropriately:
  http://cr.openjdk.java.net/~shade/shenandoah/regionsizes-getters/webrev.01/

Testing: hotspot_gc_shenandoah

Thanks,
-Aleksey