[MemorySSA] Combine verifications.

Summary:
Combine three verification methods into one to improve compile time when asserts are enabled.
Motivated by PR44066.

Sample change of timings on testcase in PR44066 (release+asserts):
MSSA off or verification disabled: 1.13s.
MSSA on (ToT): 2.48s.
With patch: 2.03s.
With enabling DefUses after combining Domination+Ordering: 2.6s.
After also combining DefUses with Domination+Ordering: 2.06s (candidate to be taken out of EXPENSIVE_CHECKS).

Subscribers: Prazek, hiraditya, george.burgess.iv, sanjoy.google, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D70618