Add support for layout requirements with layout constraints.

This commit introduces new kind of requirements: layout requirements.

This kind of requirements allows to expose that a type should satisfy certain layout properties, e.g. it should be a trivial type, have a given size and alignment, etc.

tools/swift-ide-test/ModuleAPIDiff.cpp

@@ -754,6 +754,7 @@ public:
       switch (Req.getKind()) {
       case RequirementKind::Superclass:
       case RequirementKind::Conformance:
+      case RequirementKind::Layout:
         ResultGS.ConformanceRequirements.emplace_back(
             sma::ConformanceRequirement{
                 convertToTypeName(Req.getFirstType()),