* Implement `add`, with tests.
* Implement `add_i`.
There's no test, because for whatever reason, I can't figure out how to emit this from Animate CC 2020.
* avm2: Implement `bitand` with tests.
* Implement `bitnot` with tests.
* Implement `bitor` with tests.
* avm2: Implement `bitxor`
* avm2: Implement `declocal`, `declocal_i`, `decrement`, and `decrement_i`.
* tests: `swf_approx` tests should be allowed to print NaNs.
* avm2: Implement `divide`.
* avm2: Implement `inclocal`, `inclocal_i`, `increment`, and `increment_i`.
* avm2: Implement `lshift`.
* Implement `modulo`.
* avm2: Implement `multiply` and `multiply_i` (no tests for the latter)
* avm2: Implement `negate` and `negate_i` (no tests for the latter)
* avm2: Implement `rshift`
* avm2: Implement `subtract` and `subtract_i` (the latter without tests)
* avm2: Implement `urshift`.
559bc05b6a