Move kotlin-stdlib-js project and the sources specific to the current backend to 'stdlib/js-v1' directory,
but leave sources that can be shared with the new IR backend in the common 'stdlib/js' location
with exception for 'stdlib/js/src/generated', which is used exclusively for current backend.
This simplifies sourceset configuration when building stdlib with the new backend.
Add Char.MIN_VALUE and Char.MAX_VALUE implementations in primitive companion objects.
Update builtins test data and public API.
Co-authored-by: Oskar Drozda <themppsplx@gmail.com>