Don't compute type filters inside typeof's argument

[HertzDevil]

The compiler currently computes type filters for expressions inside a typeof node's argument. However, not only do (top-level) conditionals inside typeof have no effect on the typeof itself's type, the variables inside may not even exist outside the node. For example:

if typeof(x = 1) # => Missing hash key: "x" (KeyError)
end

A less obvious example is the following, where || internally expands to if expressions:

typeof(1 || 'x') || "" # => Missing hash key: "__temp_499" (KeyError)

This PR ensures typeof's argument does not request any type filters.