Champion: verbatim interpolated string (order of $@ vs. @$) (16.3, Core 3)

This proposal will extend object initializers to allow `@$"hello"` as a verbatim interpolated string, compared to `$@"hello"` (current interpolated verbatim string).

- [ ] Proposal added
- [x] Discussed in LDM (2018-7-9)
- [x] Decision in LDM (let's do it, 2018-7-9)
- [ ] Finalized (done, rejected, inactive)
- [ ] Spec'ed

LDM history:
- https://github.com/dotnet/csharplang/blob/master/meetings/2018/LDM-2018-07-09.md

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Would it be possible for the order of the string interpolation and string literal identifiers to not matter?

e.g.

`var foo = $@"c:\foo\{someFile}";`

Is fine, but

`var foo = @$"c:\foo\{someFile}";`

isn't...

There's probably a good reason for it that I'm missing, but would it be possible to make the order not matter?

O/T And looking at the title, I now realise $@ v @$ looks a bit like some funky owl, which I'm pleased with.