Backport Fix #1154: Add @JSExportDescendentClasses (exports subclass ctors)

Backport: Had to fix stub project specifically for 0.5.x. Also had to
add method `decodedFullName` originally introduced in
698d69814eb250656f076eda494397e649bb0f78.

(cherry picked from commit b128e480ec8adc6bf1b095de37da725aeebe1c62)

Conflicts:

	stubs/src/main/scala/scala/scalajs/js/annotation/ExportAnnotations.scala