[Type checker] Force us to realize conformances for fully-validated decls.

Addresses a regression introduced by the request-evaluator in multi-file
projects, where some extensions wouldn't get realized until they are needed
in IR generation.

Author: DougGregor

lib/Sema/TypeCheckDecl.cpp

@@ -4493,7 +4493,6 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
     TC.computeAccessLevel(ED);
 
     checkUnsupportedNestedType(ED);
-
     TC.validateDecl(ED);
     TC.DeclsToFinalize.remove(ED);
     ED->setHasValidatedLayout();
@@ -4518,6 +4517,8 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
       checkEnumRawValues(TC, ED);
     }
 
+    ED->getAllConformances();
+
     TC.checkDeclCircularity(ED);
     TC.ConformanceContexts.push_back(ED);
   }
@@ -4540,6 +4541,8 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
     TC.checkDeclAttributes(SD);
     checkAccessControl(TC, SD);
 
+    SD->getAllConformances();
+
     TC.checkDeclCircularity(SD);
     TC.ConformanceContexts.push_back(SD);
   }
@@ -4765,6 +4768,8 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
 
     }
 
+    CD->getAllConformances();
+
     TC.checkDeclAttributes(CD);
     checkAccessControl(TC, CD);