Swift SIL: add a utility protocol BridgedRandomAccessCollection

It fixes the default reflection for bridged random access collections, which usually have a `bridged` stored property.
Conforming to this protocol displays the "real" children of a bridged random access collection and not just `bridged`.

Author: eeckstein

SwiftCompilerSources/Sources/SIL/Utils.swift

@@ -131,6 +131,20 @@ extension FormattedLikeArray {
   }
 }
 
+/// RandomAccessCollection which bridges to some C++ array.
+///
+/// It fixes the default reflection for bridged random access collections, which usually have a
+/// `bridged` stored property.
+/// Conforming to this protocol displays the "real" children  not just `bridged`.
+public protocol BridgedRandomAccessCollection : RandomAccessCollection, CustomReflectable {
+}
+
+extension BridgedRandomAccessCollection {
+  public var customMirror: Mirror {
+    Mirror(self, children: self.map { (label: nil, value: $0 as Any) })
+  }
+}
+
 /// A Sequence which is not consuming and therefore behaves like a Collection.
 ///
 /// Many sequences in SIL and the optimizer should be collections but cannot