feat: JS AstNodes over oxc's tree

ast_nodes.rs gives the printer oxc's view of a node's surroundings,
from the node tables rather than from bun's tree: a variant is an oxc
kind with the handle that the printer formats it from. The
ChainExpression of an optional chain, and the FunctionBody and
ExpressionStatement of an arrow with an expression body, which oxc's
parser doesn't have, are made up as oxc's formatter has them. Node gets
bun's helpers: as_expr, span, owner_or_self and the like.