[Diagnostics] Attempt .rawValue fix only if both types are equally optional

This is a follow-up to #35072.

Let's wait until both sides are equally optional before attempting
`.rawValue` fix, otherwise there is a risk that a valid code would
get diagnosed.

Extend test coverage of possible `.rawValue` situations to
contextual and argument positions to make sure that valid
code is accepted.

Resolves: SR-13951

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -4263,13 +4263,18 @@ bool ConstraintSystem::repairFailures(
       break;
     }
 
-    if (repairByUsingRawValueOfRawRepresentableType(lhs, rhs))
-      break;
-
     if (repairViaOptionalUnwrap(*this, lhs, rhs, matchKind, conversionsOrFixes,
                                 locator))
       break;
 
+    // Let's wait until both sides are of the same optionality before
+    // attempting `.rawValue` fix.
+    if (hasConversionOrRestriction(ConversionRestrictionKind::ValueToOptional))
+      break;
+
+    if (repairByUsingRawValueOfRawRepresentableType(lhs, rhs))
+      break;
+
     // If there are any restrictions here we need to wait and let
     // `simplifyRestrictedConstraintImpl` handle them.
     if (llvm::any_of(conversionsOrFixes,

test/Constraints/sr13951.swift

@@ -29,8 +29,16 @@ func aTransformer(input: Int) -> TheEnum {
 func theProblem(input: Int?) {
   var enumValue: TheEnum?
 
+  func test_arg_position(_: TheEnum?) {}
+
   if let input = input {
     enumValue = aTransformer(input: input) // Ok
+    let _: TheEnum? = enumValue // Ok
+    let _: TheEnum? = aTransformer(input: input)  // Ok
+    let _: TheEnum?? = enumValue // Ok
+    let _: TheEnum?? = aTransformer(input: input)  // Ok
+    test_arg_position(aTransformer(input: input)) // Ok
+    test_arg_position(enumValue) // Ok
   }
 
   _ = enumValue // To silence the warning