Use Contains{Any} in Regex source generator (#112065)

Author: MihaZupan

src/libraries/System.Text.RegularExpressions/gen/RegexGenerator.Emitter.cs

@@ -4079,11 +4079,13 @@ void EmitSingleCharRepeater(RegexNode node, bool emitLengthCheck = true)
 
                     // If we're able to vectorize the search, do so. Otherwise, fall back to a loop.
                     // For the loop, we're validating that each char matches the target node.
-                    // For IndexOf, we're looking for the first thing that _doesn't_ match the target node,
+                    // For Contains{Any}, we're looking for the first thing that _doesn't_ match the target node,
                     // and thus similarly validating that everything does.
                     if (TryEmitIndexOf(requiredHelpers, node, useLast: false, negate: true, out _, out string? indexOfExpr))
                     {
-                        using (EmitBlock(writer, $"if ({sliceSpan}.Slice({sliceStaticPos}, {iterations}).{indexOfExpr} >= 0)"))
+                        string containsExpr = indexOfExpr.Replace("IndexOf", "Contains");
+
+                        using (EmitBlock(writer, $"if ({sliceSpan}.Slice({sliceStaticPos}, {iterations}).{containsExpr})"))
                         {
                             Goto(doneLabel);
                         }