[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/AST/Module.cpp

@@ -1797,7 +1797,7 @@ static ProtocolConformanceRef getBuiltinMetaTypeTypeConformance(
 
   // Only metatypes of Copyable types are Copyable.
   if (protocol->isSpecificProtocol(KnownProtocolKind::Copyable) &&
-      !metatypeType->getInstanceType()->isPureMoveOnly()) {
+      !metatypeType->getInstanceType()->isNoncopyable()) {
     return ProtocolConformanceRef(
         ctx.getBuiltinConformance(type, protocol,
                                   BuiltinConformanceKind::Synthesized));