Added SingleFileTranslationTest#checkFooBoxIsOk without arguments which use test name as filename.
Make nullable check less verbose in JS-backend.
For check what variable is equal null or undefined enough to compare with null (or undefined).
See ECMAScript specification 11.9.1, 11.9.2, 11.9.3
Added support spread operator in JS-Backend.
Introduced the cache of temporary variables and expressions.
Used the cached temporary variables in SafeCall and SureCall instead create a new temporary variable.