* fix VM uint conversion bug, stricter int gen on JS
fixes#19929
* fix float -> uint64 conversion too
* no need to mask to source type
* simpler diff with explanation, add test for described issue
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)