SI-6967 Fix ClassTag unapply for primitives

This commit fixes the behavior of ClassTag's Any-accepting unapply
overload. Previously, ClassTag had overloads of unapply that accepted
all of the Java primitive aliases (language-supported magic classes
extending AnyVal), as well as an implementation that accepted an Any.
All of the AnyVal-accepting (more specific) versions of the methods
worked correctly. However, the Any-accepting version incorrectly handled
these types. For example, ClassTag.Int.unapply(3) would return Some(3)
(through the Int-accepting overload), while ClassTag.Int.unapply(3: Any)
would return None (through the Any-accepting overload). This commit
unifies these behaviors, making ClassTag.Int.unapply(3: Any) return
Some(3). It accomplishes this by adding a pattern match on the type of
that method's argument, which will delegate to one of the
more-specifically-typed overloads if possible. It also improves the
formatting of the code a bit.

One thing to note (though I doubt anyone will ever do this based on this
message) is that the AnyVal-subtype-accepting overloads should be
removed in Scala 2.12, as they are unneeded. I placed a  note to this
effect into the code.
Merge pull request #3806 from clhodapp/fix/SI-6967

SI-6967 Fix ClassTag unapply for primitives