Firefox 148 / Safari 15.6 support Legacy RegExp features (#28999)

Author: hamishwillee

javascript/builtins/RegExp.json

@@ -161,6 +161,46 @@
               "standard_track": true,
               "deprecated": true
             }
+          },
+          "rexexp_legacy_features": {
+            "__compat": {
+              "description": "Throws `TypeError` when used in `RegExp` subclass or with cross-realm mismatch.",
+              "support": {
+                "bun": {
+                  "version_added": false
+                },
+                "chrome": {
+                  "version_added": false
+                },
+                "chrome_android": "mirror",
+                "deno": {
+                  "version_added": false
+                },
+                "edge": "mirror",
+                "firefox": {
+                  "version_added": "148"
+                },
+                "firefox_android": "mirror",
+                "nodejs": {
+                  "version_added": false
+                },
+                "oculus": "mirror",
+                "opera": "mirror",
+                "opera_android": "mirror",
+                "safari": {
+                  "version_added": "15.6"
+                },
+                "safari_ios": "mirror",
+                "samsunginternet_android": "mirror",
+                "webview_android": "mirror",
+                "webview_ios": "mirror"
+              },
+              "status": {
+                "experimental": false,
+                "standard_track": false,
+                "deprecated": true
+              }
+            }
           }
         },
         "dotAll": {