Rewrote V3LifePost to not depend on having AstAssignPre and
AstAssignPost types, but work with generic AstNodeAssign. There is an
extra flag in AstVarScope to denote it's part of an NBA and should be
considered.
Step towards #6280.
No functional change.
This patch is just cleanup with some non-functional changes to enable
the next patch. Most importantly createDlyOnSet, which implements NBAs
for arrays, has a new streamlined implementation that does the same
thing. Some output code is perturbed due to statement/local variable
insertion order.
Also renamed Vdlyvfoo to VdlyFoo for easier readability of the generated
code.