* Expose if a Binary/Unary operator was 'Lifted' at the IExpression level.

* Update public API.

* Share computed value.

* Remove unnecessary extension.

* Update test code.

* Remove extension method.

* Fixup tests.

* Fixup tests.

* Fixup tests.

* Fix instances of Invalid operations with nullable

* Compound assignments also need to state if they're lifted.

* Move tests.

* Move tests.

* Move tests.

* Simplify comment.

* Case things consistently.

* Use F instead of Foo.  Because Foo is bad.