Merge #5711

5711: Display snippet in the completion label r=matklad a=SomeoneToIgnore

Before, the completion did not show the actual snippet and it was hard to understand what to input to get the right snippet:

<img width="467" alt="image" src="https://user-images.githubusercontent.com/2690773/89941040-21f6a600-dc23-11ea-94b8-61f77f88feaf.png">
<img width="367" alt="image" src="https://user-images.githubusercontent.com/2690773/89941046-23c06980-dc23-11ea-8034-6c4e14357c94.png">

Now it's more clear:

<img width="315" alt="image" src="https://user-images.githubusercontent.com/2690773/89941124-42befb80-dc23-11ea-9fcc-5fd49cc92b74.png">
<img width="210" alt="image" src="https://user-images.githubusercontent.com/2690773/89941132-4488bf00-dc23-11ea-99c2-12ec66e0a044.png">

Co-authored-by: Kirill Bulatov <mail4score@gmail.com>