Parser: Add more metadata to parsed AST nodes

[bakkdoor]

Use rogato_common::ast::NodeFactory in parser via rogato_parser::ParserContext and assign each node a unique ID for easier handling down the road (e.g. in type-checker for storing & looking up types of ast::Expression nodes.

We should also store the source location (file, line and columns) for each node to improve error reporting during type checking, codegen or even in the interpreter.