The code generation uses a mixture of literal `\n` characters and `appendln`. The latter insert `\r\n` on Windows by default, causing generated files to contain a mixture of line endings.
This commit sets the `line.separator` system property for the generator to `\n` so that `appendln` will never insert `\r` characters. As an additional measure, `.gitattributes` files were added to checkout generated stdlib files always with LF line endings.
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.