Transformer throwing Errors kills the TypeScript language server

[sam-goodwin]

Currently, when the TypeScript transformer encounters a node it does not understand, we just throw an Error and display the syntax (text) that could not be processed. This is not too big of a deal when running tsc, but it kills the language server when editing in VS code.

Instead, the transformer should not throw and instead output a NullLiteral or ErrorNode to the AST.

For errors, we will rely on a language service plugin (see: #10) to add domain-specific diagnostics instead of throwing an error.