Fix missing code sections in Selectable (#15994)

This was particularly bad since
`def applyDynamic(name: String, paramClasses: Class[_]*)(args: Any*):
Any`
Showed up as
`def applyDynamic(name: String, paramClasses: Class[_])(args: Any): Any`
With some italics

Author: Sporarum

library/src/scala/Selectable.scala

@@ -6,19 +6,19 @@ package scala
  *
  *  Implementation classes should define, or make available as extension
  *  methods, the following two method signatures:
- *
+ *  {{{
  *    def selectDynamic(name: String): Any
  *    def applyDynamic(name: String)(args: Any*): Any =
- *
+ *  }}}
  *  `selectDynamic` is invoked for simple selections `v.m`, whereas
  *  `applyDynamic` is invoked for selections with arguments `v.m(...)`.
  *  If there's only one kind of selection, the method supporting the
  *  other may be omitted. The `applyDynamic` can also have a second parameter
  *  list of `java.lang.Class` arguments, i.e. it may alternatively have the
  *  signature
- *
+ *  {{{
  *    def applyDynamic(name: String, paramClasses: Class[_]*)(args: Any*): Any
- *
+ *  }}}
  *  In this case the call will synthesize `Class` arguments for the erasure of
  *  all formal parameter types of the method in the structural type.
  */
@@ -39,9 +39,9 @@ object Selectable:
   /** A marker trait for subclasses of `Selectable` indicating
    *  that precise parameter types are not needed for method dispatch. That is,
    *  a class inheriting from this trait and implementing
-   *
+   *  {{{
    *     def applyDynamic(name: String, paramTypes: Class[_]*)(args: Any*)
-   *
+   *  }}}
    *  should dispatch to a method with the given `name` without having to rely
    *  on the precise `paramTypes`. Subtypes of `WithoutPreciseParameterTypes`
    *  can have more relaxed subtyping rules for refinements. They do not need