[CSSimplify] Detect and diagnose conformance failures related to AnyHashable conversion

Failure of an argument to AnyHashable parameter to conform to Hashable
protocol should be detected in `simplifyConformsToConstraint` and fixed
there.

Doing so requires impact assessment adjustment because regular conformance
requirements have default impact of 1, this is going to have argument
impact of 2 not avoid clashing with other failures.

test/Constraints/diagnostics.swift

@@ -661,10 +661,7 @@ example21890157.property = "confusing"  // expected-error {{value of optional ty
 
 
 struct UnaryOp {}
-
 _ = -UnaryOp() // expected-error {{unary operator '-' cannot be applied to an operand of type 'UnaryOp'}}
-// expected-note@-1 {{overloads for '-' exist with these partially matching parameter lists: (Double), (Float)}}
-
 
 // <rdar://problem/23433271> Swift compiler segfault in failure diagnosis
 func f23433271(_ x : UnsafePointer<Int>) {}
@@ -1551,3 +1548,12 @@ func rdar86611718(list: [Int]) {
   String(list.count())
   // expected-error@-1 {{cannot call value of non-function type 'Int'}}
 }
+
+// rdar://108977234 - failed to produce diagnostic when argument to AnyHashable parameter doesn't conform to Hashable protocol
+do {
+  struct NonHashable {}
+
+  func test(result: inout [AnyHashable], value: NonHashable) {
+    result.append(value) // expected-error {{argument type 'NonHashable' does not conform to expected type 'Hashable'}}
+  }
+}