[nfc] rename or eliminate isPureMoveOnly APIs

I think from SIL's perspective, it should only worry about whether the
type is move-only. That includes MoveOnlyWrapped SILTypes and regular
types that cannot be copied.

Most of the code querying `SILType::isPureMoveOnly` is in SILGen, where
it's very likely that the original AST type is sitting around already.
In such cases, I think it's fine to ask the AST type if it is
noncopyable. The clarity of only asking the ASTType if it's noncopyable
is beneficial, I think.

lib/Sema/CSSimplify.cpp

@@ -3865,7 +3865,7 @@ ConstraintSystem::matchExistentialTypes(Type type1, Type type2,
   }
 
   // move-only types (and their metatypes) cannot match with existential types.
-  if (type1->getMetatypeInstanceType()->isPureMoveOnly()) {
+  if (type1->getMetatypeInstanceType()->isNoncopyable()) {
     // tailor error message
     if (shouldAttemptFixes()) {
       auto *fix = MustBeCopyable::create(*this,
@@ -11842,7 +11842,7 @@ ConstraintSystem::simplifyBridgingConstraint(Type type1,
 
   // Move-only types can't be involved in a bridging conversion since a bridged
   // type assumes the ability to copy.
-  if (type1->isPureMoveOnly()) {
+  if (type1->isNoncopyable()) {
     return SolutionKind::Error;
   }