Support Go's "`" literals (plain string)

https://blog.golang.org/strings "UTF-8 and string literals"

```
derp = `${hello}` # should be a string where "${hello}" is the value
```

Basically a way to disable all interpolation and processing, everything between the "`" should be as-in, unprocessed

Was one of the biggest pain points we've had doing https://github.com/seatgeek/hashi-helper where we had to escape a ton HCL sensitive characters in passwords and other inputs

The issue names no files or tests. Start with the linked Go string-literal reference and the `${hello}` example; done means backtick-delimited content remains exactly as written and is not interpolated or otherwise processed.

Written by the indexing model from the issue text.