If an accessor is not available at runtime we fall back
to the property access.
This is useful in cases when JS objects are casted to Kotlin
classes implicitly. This pattern did work in the old BE, which
lead to a significant amount of code which doesn't work anymore.
Fixed by outlining JS code that uses Kotlin variables making usages of
these locals explicit and preventing bugs due to one-sided variable renaming.
This prevents using Kotlin variables as lvalue in JS code.
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.
Artem Kobzar