Allow emoji without surrounding `` as variable names

I propose we support directly using emoji in variable names

The existing way of approaching this problem in F# is same as having space in variable names

There's no down side to this, nothing is going to break

The advantage of making this adjustment is ease of use

The disadvantages of making this adjustment is nothing

Please tick this by placing a cross in the box:
* [x] This is not a question (e.g. like one you might ask on [stackoverflow](http://stackoverflow.com)) and I have searched stackoverflow for discussions of this issue
* [x] I have [searched both open and closed suggestions on this site](http://github.com/fsharp/fslang-suggestions/issues) and believe this is not a duplicate
* [x] This is not something which has obviously "already been decided" in previous versions of F#. If you're questioning a fundamental design decision that has obviously already been taken (e.g. "Make F# untyped") then please don't submit it.

Please tick all that apply:
* [x] This is not a breaking change to the F# language design
* [ ] I or my company would be willing to help implement and/or test this

## For Readers

If you would like to see this issue implemented, please click the :+1: emoji on this issue. These counts are used to generally order the suggestions by engagement.

No files, tests, or entry points are named in the issue. Review the existing F# rules for identifiers and the treatment of names containing spaces, then determine the required language-design scope and tests needed to establish support for unquoted emoji variable names.

Written by the indexing model from the issue text.