Use final vals where possible in javalanglib.

This means in all the companions of boxed classes. This
makes the constructors of these companions elideable.

The values Float.MIN_NORMAL and Double.MIN_NORMAL have been
deleted, because there was no way to make them constant
expressions. Since they are final vals anyway in the JDK, they
will be constant-folded by scalac, so there is no need to emit
them in our library.
Lots of optimizations here and there in the library.

Review of all the javalib and the library with optimizations
in mind (and knowing what the optimizer can do).
Merge pull request #1030 from sjrd/opt-javalib

Optimizations in the library and javalib
Fix #1023: Deprecate implicit conversions to/from js.Array
Fix #1038: Remove usage of deprecated defaultSettings
Fix #1037: Deprecate packageJS and related tasks
Merge pull request #1034 from gzm0/deprecate-array-conv

Fix #1023: Deprecate implicit conversions to/from js.Array
Fix #1032: Correctly test full scalajs lib size again.

The scalajs library used to be in the `externalDependencyClasspath`
even for internal projects, due to the `useLibraryButDoNotDependOnIt`
hack. This hack was removed in commit
2e90a7b259de38ec3a19b27a37abfc759e99215a and the scalajs library moved
to the `internalDependencyClasspath`.

This commit updates the size checking scripts to test both the extdeps
and the intdeps.
Merge pull request #1043 from gzm0/deprecate-packageJS

Fix #1037: Deprecate packageJS and related tasks
Merge pull request #1042 from gzm0/remove-sbt-default-settings

Fix #1038: Remove usage of deprecated defaultSettings
Merge pull request #1041 from gzm0/fix-extdeps-check

Fix #1032: Correctly test full scalajs lib size again.
Fix #1028: A helper for Object.getClass().
Future-proof #1027: add a helper for identityHashCode().

This still returns 42 for all objects. But with this refactoring,
we'll have the possibility to change that in a completely
binary compatible way.
Merge pull request #1044 from sjrd/helpers-getclass-hashcode

Helpers for getClass and identityHashCode
wip