Move test cases to Regex.Match.Tests.cs as requested

Removed dedicated [Fact] test from RegexGeneratorParserTests.cs and added
test cases to Regex.Match.Tests.cs. The cases are already inside the guard
for non-backtracking engine (line 87), so they will be tested on all
backtracking engines including the source generator.

Co-authored-by: stephentoub <[email protected]>

Author: Copilot

src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/Regex.Match.Tests.cs

@@ -182,6 +182,10 @@ public static IEnumerable<object[]> Match_MemberData()
                 yield return (@"(?<=(abc)+?)", "123abc", RegexOptions.None, 0, 6, true, "");
                 yield return (@"(?<=(abc)+?)", "123ab", RegexOptions.None, 0, 5, false, "");
                 yield return (@"(?<=(abc)+?123)", "abcabc123", RegexOptions.None, 0, 9, true, "");
+                // Regression test for https://github.com/dotnet/runtime/issues/120882
+                // Lazy loops inside lookbehinds should generate valid code
+                yield return (@"(?<=(abc)+?123)a", "abcabc123a", RegexOptions.None, 0, 10, true, "a");
+                yield return (@"(?<=(abc)+?)a", "abca", RegexOptions.None, 0, 4, true, "a");
                 yield return (@"a+(?!c)(?<=y)", "yaab", RegexOptions.None, 0, 4, false, "");
                 yield return (@"(?<=a{2,4})b+", "aaabbb", RegexOptions.None, 0, 6, true, "bbb");
                 yield return (@"(?<=a+)b+?", "aaabbb", RegexOptions.None, 0, 6, true, "b");

src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/RegexGeneratorParserTests.cs

@@ -1233,30 +1233,5 @@ partial class C
                 return handle.Process.StandardOutput.ReadToEnd();
             }
         }
-
-        [Fact]
-        public async Task LazyLoopInLookbehind_GeneratesValidCode()
-        {
-            // Regression test for https://github.com/dotnet/runtime/issues/XXXXX
-            // Lazy loops inside lookbehinds should generate valid code with accessible backtracking labels
-            Assert.Empty(await RegexGeneratorHelper.RunGenerator(@"
-                using System.Text.RegularExpressions;
-
-                partial class C
-                {
-                    [GeneratedRegex(@""(?<=(abc)+?123)a"")]
-                    public static partial Regex LazyLoopInLookbehind1();
-
-                    [GeneratedRegex(@""xxx(?<=(abc)+?123)a"")]
-                    public static partial Regex LazyLoopInLookbehind2();
-
-                    [GeneratedRegex(@""(?<=(abc)+?123)"")]
-                    public static partial Regex LazyLoopInLookbehind3();
-
-                    [GeneratedRegex(@""(?<=(abc)+?)a"")]
-                    public static partial Regex LazyLoopInLookbehind4();
-                }
-            ", compile: true));
-        }
     }
 }