[SourceKit] Make sure we reuse ASTContext in function bodies for solver-based cursor info

The main problem that prevented us from reusing the ASTContext was that we weren’t remapping the `LocToResolve` in the temporary buffer that only contains the re-parsed function back to the original buffer. Thus `NodeFinder` couldn’t find the node that we want to get cursor info for.

Getting AST reuse to work for top-level items is harder because it currently heavily relies on the `HasCodeCompletion` state being set on the parser result. I’ll try that in a follow-up PR.

rdar://103251263

lib/IDE/CursorInfo.cpp

@@ -140,7 +140,7 @@ private:
   DeclContext *getCurrentDeclContext() { return DeclContextStack.back(); }
 
   bool rangeContainsLocToResolve(SourceRange Range) const {
-    return Range.contains(LocToResolve);
+    return getSourceMgr().containsRespectingReplacedRanges(Range, LocToResolve);
   }
 
   PreWalkAction walkToDeclPre(Decl *D) override {