Add asymmetric equality tester to match a string against a regexp

- Also move the asymmetric testers into their own dir for easier
  locating.

[#58120558] Fix #243

src/core/asymmetric_equality/StringMatching.js

@@ -0,0 +1,16 @@
+getJasmineRequireObj().StringMatching = function(j$) {
+
+  function StringMatching(expected) {
+    if (!j$.isString_(expected) && !j$.isA_('RegExp', expected)) {
+      throw new Error('Expected is not a String or a RegExp');
+    }
+
+    this.regexp = new RegExp(expected);
+  }
+
+  StringMatching.prototype.asymmetricMatch = function(other) {
+    return this.regexp.test(other);
+  };
+
+  return StringMatching;
+};