Use isQualifierConvertible in isInputRange!(R, E)

This replaces the bespoke type comparison that was previously used. All
conversions allowed by the previous version are still allowed after this
change.

std/range/primitives.d

@@ -165,21 +165,24 @@ See_Also:
 
 Params:
  R = type to be tested
- E = the type of the elements of the range if not `void`
+ E = if present, the elements of the range must be
+ $(DDSUBLINK spec/const3, implicit_qualifier_conversions, qualifier-convertible)
+ to this type
 
 Returns:
  `true` if R is an input range (possibly with element type `E`), `false` if not
  */
-enum bool isInputRange(R, E = void) =
+enum bool isInputRange(R) =
  is(typeof(R.init) == R)
  && is(typeof((R r) { return r.empty; } (R.init)) == bool)
  && (is(typeof((return ref R r) => r.front)) || is(typeof(ref (return ref R r) => r.front)))
  && !is(typeof((R r) { return r.front; } (R.init)) == void)
- && is(typeof((R r) => r.popFront))
- && (is(E == void) ||
- is(ElementType!R == E) ||
- is(const(ElementType!R) == E) ||
- (is(const(ElementType!R) == immutable E) && is(const(E) == E)));
+ && is(typeof((R r) => r.popFront));
+
+/// ditto
+enum bool isInputRange(R, E) =
+ .isInputRange!R && isQualifierConvertible!(ElementType!R, E);
+
 ///
 @safe unittest
 {