Rework the serialization schema for conformances and requirements.

We now schedule conformance emissions in basically the same way
we do for types and declarations, which means that we'll emit them
uniquely in the module file instead of redundantly at every use.
This should produce substantially smaller module files overall,
especially for modules that heavily use generics.  It also means
that we can remove all the unfortunate code to support using
different abbrev codes for them in different bitcode blocks.

Requirement lists are now emitted inline in the records that need
them instead of as trailing records.  I think this will improve
space usage, but mostly it assists in eliminating the problem
where abbrev codes are shared between blocks.

Author: rjmccall

lib/Serialization/DeclTypeRecordNodes.def

@@ -127,7 +127,6 @@ DECL(OPAQUE_TYPE)
 DECL(PATTERN_BINDING)
 DECL(PROTOCOL)
 TRAILING_INFO(DEFAULT_WITNESS_TABLE)
-TRAILING_INFO(PROTOCOL_TYPEALIAS)
 TRAILING_INFO(ASSOCIATED_TYPE)
 DECL(PREFIX_OPERATOR)
 DECL(POSTFIX_OPERATOR)
@@ -172,8 +171,8 @@ OTHER(TOP_LEVEL_CODE_DECL_CONTEXT, 223)
 
 OTHER(GENERIC_PARAM_LIST, 230)
 OTHER(GENERIC_SIGNATURE, 231)
-TRAILING_INFO(GENERIC_REQUIREMENT)
-TRAILING_INFO(LAYOUT_REQUIREMENT)
+OTHER(REQUIREMENT_SIGNATURE, 232)
+// 233 is unused; was LAYOUT_REQUIREMENT
 OTHER(BUILTIN_PROTOCOL_CONFORMANCE, 234)
 OTHER(SIL_GENERIC_SIGNATURE, 235)
 OTHER(SUBSTITUTION_MAP, 236)
@@ -182,14 +181,14 @@ OTHER(LOCAL_DISCRIMINATOR, 237)
 OTHER(PRIVATE_DISCRIMINATOR, 238)
 OTHER(FILENAME_FOR_PRIVATE, 239)
 
-OTHER(ABSTRACT_PROTOCOL_CONFORMANCE, 240)
+// 240 is unused; was ABSTRACT_PROTOCOL_CONFORMANCE
 OTHER(NORMAL_PROTOCOL_CONFORMANCE, 241)
 OTHER(SPECIALIZED_PROTOCOL_CONFORMANCE, 242)
 OTHER(INHERITED_PROTOCOL_CONFORMANCE, 243)
-OTHER(INVALID_PROTOCOL_CONFORMANCE, 244)
+// 244 is unused; was INVALID_PROTOCOL_CONFORMANCE
 
 OTHER(SIL_LAYOUT, 245)
-OTHER(NORMAL_PROTOCOL_CONFORMANCE_ID, 246)
+// 246 is unused; was NORMAL_PROTOCOL_CONFORMANCE_ID
 OTHER(PROTOCOL_CONFORMANCE_XREF, 247)
 OTHER(MEMBERS, 248)
 OTHER(XREF, 249)