Add validation for with nodes to match if, while, assert

[sirosen]

I believe that after v1.5.0 , with nodes are the only case of a keyword followed by an expression with

• optional space after the keyword
• missing validation that some non-empty whitespace is present on non-parenthesized expressions

---

I have some codepaths in my fixer for removing extra parens.
I found that after 1.5.0, if(x()) fixing failed because it removes the parens first, then adds the space. It generates ifx() in an intermediate state and is rejected.

The same path works for with(x()), removing parens (producing withx()) and then adding the space (with x()).

This isn't a problem for me, but I think it would be better for these APIs to be as consistent as we can have them! 🙂