tools & vcl: move OutputDevice::ImplRotatePos() to Point::RotateAbout()

OutputDevice has a private function that rotates a point around another
point. However, there is no real reason why OutputDevice should be
responsible for this - it's really the responsibility of the Point
class in the tools module. Therefore, I've moved this functionality out
of OutputDevice and into Point, but I've renamed it from the rather
confusing name "ImplRotatePos" to "RotateAround", which is what it
actually does.

Change-Id: If12fb40a7b476653224d4edfc01887bc91a80c7d
Reviewed-on: https://gerrit.libreoffice.org/12171
Reviewed-by: Chris Sherlock <chris.sherlock79@gmail.com>
Tested-by: Chris Sherlock <chris.sherlock79@gmail.com>