Apply generic metadata patterns to all types and change their layout.

The layout changes to become relative-address based.  For this to be
truly immutable (at least on Darwin), things like the RO data patterns
must be moved out of the pattern header.  Additionally, compress the
pattern header so that we do not include metadata about patterns that
are not needed for the type.

Value metadata patterns just include the metadata kind and VWT.

The design here is meant to accomodate non-default instantiation
patterns should that become an interesting thing to support in the
future, e.g. for v-table specialization.

Author: rjmccall

include/swift/ABI/MetadataValues.h

@@ -1177,6 +1177,47 @@ enum class GenericRequirementLayoutKind : uint32_t {
   Class = 0,
 };
 
+/// Flags used by generic metadata patterns.
+class GenericMetadataPatternFlags : public FlagSet<uint32_t> {
+  enum {
+    // All of these values are bit offsets or widths.
+    // General flags build up from 0.
+    // Kind-specific flags build down from 31.
+
+    /// Does this pattern have an extra-data pattern?
+    HasExtraDataPattern = 0,
+
+    // Class-specific flags.
+
+    /// Does this pattern have an immediate-members pattern?
+    Class_HasImmediateMembersPattern = 31,
+
+    // Value-specific flags.
+
+    /// For value metadata: the metadata kind of the type.
+    Value_MetadataKind = 21,
+    Value_MetadataKind_width = 11,
+  };
+
+public:
+  explicit GenericMetadataPatternFlags(uint32_t bits) : FlagSet(bits) {}
+  constexpr GenericMetadataPatternFlags() {}
+
+  FLAGSET_DEFINE_FLAG_ACCESSORS(Class_HasImmediateMembersPattern,
+                                class_hasImmediateMembersPattern,
+                                class_setHasImmediateMembersPattern)
+
+  FLAGSET_DEFINE_FLAG_ACCESSORS(HasExtraDataPattern,
+                                hasExtraDataPattern,
+                                setHasExtraDataPattern)
+
+  FLAGSET_DEFINE_FIELD_ACCESSORS(Value_MetadataKind,
+                                 Value_MetadataKind_width,
+                                 MetadataKind,
+                                 value_getMetadataKind,
+                                 value_setMetadataKind)
+};
+
 } // end namespace swift
 
 #endif /* SWIFT_ABI_METADATAVALUES_H */