[Sema] Generate TRC for unparsed functions right before type-checking

Fix an issue where `if #available(...)` conditions were ignored in
emit-module-separately builds or when skipping non-inlinable function
bodies.

To handle functions for which parsing is delayed but type-checking is
not delayed, move up building the delayed TRC to the
TypeCheckFunctionBodyRequest service.

rdar://83166742

lib/AST/Module.cpp

@@ -2892,7 +2892,7 @@ SynthesizedFileUnit &SourceFile::getOrCreateSynthesizedFile() {
   return *SynthesizedFile;
 }
 
-TypeRefinementContext *SourceFile::getTypeRefinementContext() {
+TypeRefinementContext *SourceFile::getTypeRefinementContext() const {
   return TRC;
 }