[rbi] When finding closure uses in an immediately invoked closure, distinguish in between captures and parameters.

Otherwise, when one diagnoses code like the following:

```
Task {
  {
    use($0)
  }(x)
}
```

One gets that $0 was captured instead of x. Unfortunately, since function
parameters do not have locations associated with them, we do not mark x
itself... instead, we mark the closure... which is unfortunate.

Author: gottesmm

lib/SILOptimizer/Mandatory/SendNonSendable.cpp

@@ -294,14 +294,16 @@ findClosureUse(Operand *initialOperand) {
     // immediately invoked. In such a case, we can emit a better diagnostic in
     // the called closure.
     if (auto fas = FullApplySite::isa(op->getUser())) {
-      if (auto *f = fas.getCalleeFunction();
-          f && f->getDeclRef().getClosureExpr()) {
-        auto *fArg = f->getArgument(fas.getCalleeArgIndex(*op));
-        for (auto *use : fArg->getUses()) {
-          if (visitedOperand.insert(use).second)
-            worklist.emplace_back(use, fArg);
+      if (auto *f = fas.getCalleeFunction()) {
+        auto *fArg = cast<SILFunctionArgument>(
+            f->getArgument(fas.getCalleeArgIndex(*op)));
+        if (fArg->isClosureCapture()) {
+          for (auto *use : fArg->getUses()) {
+            if (visitedOperand.insert(use).second)
+              worklist.emplace_back(use, fArg);
+          }
+          continue;
         }
-        continue;
       }
     }
 

test/Concurrency/transfernonsendable_sending_params.swift

@@ -524,6 +524,12 @@ func taskIsolatedCaptureInSendingClosureLiteral(_ x: NonSendableKlass) {
     }()
   }
 
+  Task { // expected-warning {{passing closure as a 'sending' parameter risks causing data races between code in the current task and concurrent execution of the closure}}
+    { // expected-note {{closure captures 'x' which is accessible to code in the current task}}
+      print($0)
+    }(x)
+  }
+
   takeClosure { // expected-warning {{passing closure as a 'sending' parameter risks causing data races between code in the current task and concurrent execution of the closure}}
     print(x) // expected-note {{closure captures 'x' which is accessible to code in the current task}}
   }