Restructure Statement::VarDecl to hold declarators: Vec<VarDeclarator>
instead of a single target/init pair, enabling `var a = 1, b = 2;`
syntax. Extract shared parse_var_declarators() helper used by both
statement-level declarations and for-loop headers, fixing a pre-existing
bug where destructuring patterns without initializers in for-loop
additional declarators were silently accepted.
Also add Expr::Sequence for the comma operator (a, b, c) and wire
parse_expression() into all grammar positions that accept a full
Expression production.
Promotes 6 JS262 conformance tests from known_fail to pass.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
cb0e35b01c