Refactor operator documentation generation for primitives and unsigned
types so that it is easier to specialize it.
Manually sync docs of numeric types in js-ir stdlib.
KT-26234
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.
Ilya Gorbunov