ConstantAnnotation has unnecessary restrictions due to its Java heritage #11724
Description
For example, named arguments need to be used unless therese one single parameter called value. We should implement this restirction only for Java annotations.
scala> class a(x: Int) extends annotation.ConstantAnnotation
defined class a
scala> @a(1) val x = 0
^
error: arguments to Java annotations or subclasses of ConstantAnnotation have to be supplied as named arguments
^
error: annotation a is missing argument x
scala> class a(value: Int) extends annotation.ConstantAnnotation
defined class a
scala> @a(1) val x = 0
x: Int = 0