Add runtime type modifications

[ClickerMonkey]

Expressions can refine types, so any following Expressions will see the new type:

So if a type is an optional text, we can use var is defined and if that expression is true it can modify the var type from optional text to text.

The Or expression complicates this, it takes each type modification and converts modifications on the same var to Many.
For example if (x is Text or x is Boolean) { // x is Many<Text | Boolean> }.

Certain expressions have a condition (like If, or the IIF operation) so inside the "true" expression the types are modified.