Move regexp implementation into its own folder.

src/interpreter-irregexp.h

-// Copyright 2011 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-// A simple interpreter for the Irregexp byte code.
-
-#ifndef V8_INTERPRETER_IRREGEXP_H_
-#define V8_INTERPRETER_IRREGEXP_H_
-
-namespace v8 {
-namespace internal {
-
-
-class IrregexpInterpreter {
- public:
-  static RegExpImpl::IrregexpResult Match(Isolate* isolate,
-                                          Handle<ByteArray> code,
-                                          Handle<String> subject,
-                                          int* captures,
-                                          int start_position);
-};
-
-
-} }  // namespace v8::internal
-
-#endif  // V8_INTERPRETER_IRREGEXP_H_