Refactoring the compiler to use transformers moves the code generation
after type-checking which suppresses the errors TypeScript would
generate in the user code.
`TypeChecker` currently produces the same factory code that was
generated prior the switch to transfomers, getting back the same
diagnostics as before. The refactoring will allow the code to
diverge from the factory code and allow better diagnostic error
messages than was previously possible by type-checking the factories.
Template expressions can now use a post-fix `!` operator
that asserts the target of the operator is not null. This is
similar to the TypeScript non-null assert operator. Expressions
generated in factories will be generated with the non-null assert
operator.
Closes: #10855
Victor Berchet
Chuck Jazdzewski
Tobias Bosch