Go: add raw string literal syntax

[nicot]

Go allows raw string literals using backquotes:
https://golang.org/ref/spec#String_literals

I'm not sure what the rules are on escaping inside raw string literals. This PR could be a starting point.

Thanks!

[msftclas]

Hi @nicot, I'm your friendly neighborhood Microsoft Pull Request Bot (You can call me MSBOT). Thanks for your contribution!

This seems like a small (but important) contribution, so no Contribution License Agreement is required at this point. Real humans will now evaluate your PR.

TTYL, MSBOT;

[alexdima]

@nicot Can you also please add some tests for this in https://github.com/Microsoft/monaco-languages/blob/master/test/go.test.ts

[nicot]

I've added a test for the raw string literal syntax.

Anything else I can do?

[alexdima]

Brilliant! Thank you for your contribution!