RFR (XS) 8232729: Shenandoah: assert ShenandoahHeap::cas_oop addresses are aligned

[Aleksey Shipilev]

RFE:
  https://bugs.openjdk.java.net/browse/JDK-8232729

Fix:
  https://cr.openjdk.java.net/~shade/8232729/webrev.01/

Current ShenandoahHeap::cas_oop routines perform CASes on given address, hoping the hardware would
handle it properly. In most cases, this is guaranteed by callers who pass aligned addresses to it:
those are aligned narrowOop*/oop* fields or the roots that we can update concurrently.

However, we should assert the alignment directly to catch bugs. This would fail the asserts with
proper message rather than obscure SIGBUS on some platforms like AArch64. These new asserts are
known to legitimately fail with Traversal (JDK-8232730) on x86_64 and with jcstress on AArch64
(JDK-8232712), so I am going to push this after the fixes land to ensure clean test results.

Testing: {x86_64, x86_32} hotspot_gc_shenandoah; x86_64 tier1 with Shenandoah (running)

-- 
Thanks,
-Aleksey