refactor: work in progress on Expr based NominalPhrase

[hippietrail]

Issues

N/P

Description

The Pattern version NominalPhrase has some quirks and limitations and is pretty hard to work on.
This PR introduces an Expr version of NominalPhrase built on SequenceExpr.

How Has This Been Tested?

The Pattern's unit tests all pass using the Expr version.
Some unit tests that should pass but do are added to the Pattern to illustrate some of its deficiencies.
Some unit tests that wouldn't work with the Pattern but do with the Expr are added.

So far the Expr is only used in the linters and other Exprs. There's a few other places the Pattern is still used that have to be switched over.

Checklist

• I have performed a self-review of my own code
• I have added tests to cover my changes