Regression: Search with regular expressions is broken.

[testing-in-chrome]

• VSCode Version: 1.19.1
• OS Version: Debian Testing / Ubuntu 16.04

Steps to Reproduce:

1. Create a file with the following text in it:

// Copyright 2017 MyProject
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

2. Go to the Search tab, enable regex search, and type:
   // Copyright 2017[\s\S]*the License.

--->> vscode doesn't find anything.
--->> It should find the entire text above.

Reproduces without extensions: Yes.

[roblourens]

Multiline search isn't supported, this isn't a regression: #13155