Reduce number of attrs for #[visited_node] used by AST codegen

[overlookmotel]

Currently:

#[visited_node]
pub enum Expression<'a> {
    #[visit_args(flags = ScopeFlags::Function)]
    FunctionExpression(Box<'a, Function<'a>>),
    /* ... */
}

#[visited_node]
pub struct TryStatement<'a> {
    /* ... */
    #[visit_as(FinallyClause)]
    pub finalizer: Option<Box<'a, BlockStatement<'a>>>,
}

Could we reduce the number of "special" attrs by changing visit_args(...) / visit_as(...) to visit(args(...)) / visit(as(...))?

#[visited_node]
pub enum Expression<'a> {
    #[visit(args(flags = ScopeFlags::Function))]
    FunctionExpression(Box<'a, Function<'a>>),
    /* ... */
}

#[visited_node]
pub struct TryStatement<'a> {
    /* ... */
    #[visit(as(FinallyClause))]
    pub finalizer: Option<Box<'a, BlockStatement<'a>>>,
}

@rzvxa What do you think? Not a big deal, but I think it'd be neater. I suspect we may end up adding more attrs later on (it may be useful, for instance, to tag all TS-only fields #[typescript]) and it could get out of hand.

[rzvxa]

Good idea, I added the visit_args, and when the need for visit_as was raised I just copied the parsing of the previous one. I'll merge them together.

[overlookmotel]

Implemented in #4371.