[tests] Adding SR-12383 regression test

Author: LucianoPAlmeida

test/Constraints/sr12383.swift

@@ -0,0 +1,15 @@
+// RUN: %target-typecheck-verify-swift
+
+protocol Protocol {
+  associatedtype Index: Comparable
+  subscript(bounds: Range<Index>) -> Int { get }
+  // expected-note@+1 {{protocol requires subscript with type '(Wrapper<Base>.Index) -> Int' (aka '(Base.Index) -> Int'); do you want to add a stub?}}
+  subscript(position: Index) -> Int { get } 
+}
+
+struct Wrapper<Base: Protocol>: Protocol { // expected-error {{type 'Wrapper<Base>' does not conform to protocol 'Protocol'}}
+  typealias Index = Base.Index
+  subscript(bounds: Range<Index>) -> Int { // expected-note {{candidate has non-matching type '<Base> (Range<Wrapper<Base>.Index>) -> Int' (aka '<Base> (Range<Base.Index>) -> Int')}}
+    get { 1 }
+  }
+}