Add appropriate bounds to CountableClosedRange and CountableRange.

Previously, both CountableRange and CountableClosedRange required
their bound types to be Strideable with a Stride type that conforms to
SignedInteger. Those constraints were not present on the generic
typealiases that replaced these structs. Add them back now, which
fixes the GRDB source compatibility regression.

Fixes https://bugs.swift.org/browse/SR-6907 / rdar://problem/29066394.

Author: DougGregor

stdlib/public/core/ClosedRange.swift

@@ -479,4 +479,5 @@ extension ClosedRange {
 @available(*, deprecated, renamed: "ClosedRange.Index")
 public typealias ClosedRangeIndex<T> = ClosedRange<T>.Index where T: Strideable, T.Stride: SignedInteger
 @available(*, deprecated, renamed: "ClosedRange")
-public typealias CountableClosedRange<T: Comparable> = ClosedRange<T>
+public typealias CountableClosedRange<Bound: Strideable> = ClosedRange<Bound>
+  where Bound.Stride : SignedInteger

stdlib/public/core/Range.swift

@@ -878,5 +878,5 @@ extension Range {
 }
 
 @available(*, deprecated, renamed: "Range")
-public typealias CountableRange<Bound: Comparable> = Range<Bound>
-
+public typealias CountableRange<Bound: Strideable> = Range<Bound>
+  where Bound.Stride : SignedInteger

test/Compatibility/stdlib_generic_typealiases.swift

@@ -1,12 +1,18 @@
 // RUN: %target-typecheck-verify-swift
 
-struct RequiresComparable<T: Comparable> { }
+struct RequiresStrideable<T: Strideable> { }
 
 extension CountableRange { // expected-warning{{'CountableRange' is deprecated: renamed to 'Range'}}
   // expected-note@-1{{use 'Range' instead}}{{11-25=Range}}
-  func testComparable() {
-    _ = RequiresComparable<Bound>()
+  func testStrideable() {
+    _ = RequiresStrideable<Bound>()
   }
+
+  func foo() { }
+}
+
+extension Range {
+  func foo() { } // not a redefinition
 }
 
 struct RequiresHashable<T: Hashable> { }