Fix 'new' parsing & allow omitting parenthesis

[dcodeIO]

This fixes #932 by adding more specific code to parse new expressions, also handling new SomeClass without parenthesis.

As it stands, the parsing is not quite JS-like in that it expects an identifier or series of identifiers (combined to a property access) as the target, assuming that anything else (like new (getSomeCtor())) can't be constructed anyway in AS.

[dcodeIO]

Last commit makes it so that new takes a TypeName, not an expression anymore, potentially opening up that function test<T>(): T { return new T(); } feature we discussed in the past. It doesn't do this yet, however, just figured that if this isn't JS-like anyway, we may as well go as far.

Also cleans up quite a bit of parser code. Along with the tokenizer, the parser belongs to the oldest code we have, and it should be possible to clean it up even more with today's knowledge - but leaving that to follow-up PRs.

[MaxGraey]

It will be also great hint about constructor (it couldn't be a public or has different signature):

function test1<T extends { new(): T }>(): T {
  return new T();
}

function test1<T extends { new(a: i32): T }>(): T {
  return new T(123);
}