* Optimize lent in JS [backport:1.6]
* addr on lent doesn't work anymore, don't use it
* use unsafeAddr in test again for older versions
(cherry picked from commit 07c7a8a526)
Prefer moving tests to a non-js directory so that they get tested across all backends automatically.
Ideally, tests/js should be reserved to code that only makes sense in js.
Note also that tests for a js specific module (e.g.: std/jsbigints) belong to tests/stdlib, (e.g.: tests/stdlib/tjsbigints.nim)