Substitute underlying type from typealias

[art-divin]

Resolves #831

Context

This PR adds a type by name lookup for recognizing types hidden "behind" a typealias.

Using the following template, wrong results were produced:

<%
let foo = types.structs.first { $0.name == "Foo" }!

let bar = foo.instanceVariables.first { $0.name == "bar" }!
print(bar.type.name)
print(bar.typeName)
print(bar.typeName.actualTypeName)
%>

Query	Before	After
print(bar.type)	nil	Optional(Int)
print(bar.typeName)	Bar	Bar
print(bar.typeName.actualTypeName)	nil	Optional(Int)