Embedded subexpressions

[msftrncs]

Improve embedded substatements, fix #132.

• Rename #interpolatedStringContent to #subexpression.
• Remove include #interpolation from #subexpression.
• Change scopes in #interpolation to include meta.embedded, keyword.other was
  punctuation.definition.variable.
• Change scope in root pattern for $( ), keyword.other was
  punctuation.definition.variable. (No tests are present for this)
• Remove redundant includes from #subexpression and #interpolation.
• Adjust test, of embedded substatements in double quoted strings.

Sample appearance

• VS Code (before):
  

• VS Code:
  

• ATOM:
  

[andyleejordan]

@msftrncs Is this PR superseded by #156, or should we merge it while trying to get that one in (since it appears to be a complete rewrite)?

[msftrncs]

This was meant to be separate of #156, so that it could be benefitted from sooner. Its one of several PR's I made trying to bring in some trivial fixes quicker. This goes along with #173 and #175

[andyleejordan]

Thanks @msftrncs! After evaluating the state of the tests, CI, and these three PRs, we went ahead and merged. What's the worst that could happen? 😁

[andyleejordan]

I know it took a couple years but @msftrncs I wanted to let you know that GitHub Linguist just shipped which includes this and a few of your other fixes!