refs #6978, refs #6752, refs #21613, refs #24234
The `jsNoInt64`, `whenHasBigInt64`, `whenJsNoBigInt64` templates are
replaced with bool constants to use with `when`. Weird that I didn't do
this in the first place.
The `whenJsNoBigInt64` template was also slightly misleading. The first
branch was compiled for both no bigint64 on JS as well as on C/C++. It
seems only `trandom` depended on this by mistake.
The workaround for #6752 added in #6978 to `times` is also removed with
`--jsbigint64:on`, but #24233 was also encountered with this, so this PR
depends on #24234.
(cherry picked from commit 041098e882)
* improve test coverage for isolation
* a bit better
* rename channels to channels_builtin
* follow up #17276
* fix
* Update lib/std/private/jsutils.nim
