Cleanup the use of Double primitive wrapper

[BradWalker]

As of Java 9, the VM can do a better job of handling the conversion from a Double primitive to a Double Object or vice versa.

This is an extension of the work done in #2498.

No tests have been touched as those expressly need to manage the conversion.

A couple of places I also cleaned up the Float.

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[mbien]

@BradWalker say if you need help with this one

[neilcsmith-net]

Given we're close to freeze, let's punt this to NB16.

[neilcsmith-net]

Given we're now close to NB16 freeze and there's been no further movement on this, going to close. Re-open if necessary.