This Pull Request changes the following:
- Implement `with` statement parsing, ast node, compilation and excution.
- Implement object environments that are used in the `with` statement excution.
The implementation of object environments can probably be optimized further by using more compile-time information about when object environments can exist. Maybe there could also be a separate environment stack for object environments to reduce the filtering and iteration that is needed with the current implementation.
This does not fix all tests in the `test/language/statements/with` suite yet. But for most failing tests that I have looked at we are missing other features / have bugs elsewhere.
As a note for the review:
The functions in the `impl Context` block in `boa_engine/src/environments/runtime.rs` are mostly copied / moved from the existing functions. The only change there should be the addition of the object environment logic. They had to be moved to `Context` because of borrow semantics.