Backport new parser AST syntaxes to mainline for v1 testing support

[TwitchBronBron]

We really want to start having teams test out the v1.0.0 branch of code, but there are many places that require explicit typecasting to work (or a few other slight additions to the AST Parser).

To make it easier for teams to migrate (or even just test out) the v1 branch, it would be nice to start adding the new syntax to the master branch. So that way teams can install v1 alphas, add a bunch of type casting or other as <whatever> items in their code, then remove v1 alpha and their code still validates properly.The transpiler in master would just strip out these new AST items for now.

This would go a long way in allowing teams to test v1, and should be a minimal amount of work.

[markwpearce]

I think this is the list of syntax changes:

• typed arrays (eg. string[])
• type casts (eg. x = y as SomeType)
• allowing built-in interfaces & custom component names as types
• allowing union types (eg. sub foo(x as string or integer))

[TwitchBronBron]

Yeah that's all I can think of.

[markwpearce]

closed with #1034