Mark Device::getDPI() method as deprecated

[ShahzaibIbrahim]

The method shall be deprecated. Depending on the needs identified in the first point, a replacement may be provided or at least information about way to replace calls to the methods as applied in the first point shall be added to the deprecation notice.

This should be done after replacing all the usage in platform (see sub-tickets)

TO-Do

• Check if it's possible to deprecate a method in a superclass but leave the one in the subclass as not deprecated. ANSWER: it is possible. Additionally, no warning is issued when using the method in the subclass (as expected)
  • If it's not possible then just change the documentation of both methods in Device and in Printer.
  • If it is possible then the issue remains blocked.

[HeikoKlare]

Since we will probably (need to reasonably) keep usages of that method when the Device is a Printer, we will probably need to mark that method as deprecated for Device while still keeping it valid for the Printer subclass, won't we?

[ShahzaibIbrahim]

No, we replace it even for Printer. See eclipse-platform/eclipse.platform.swt#1802

[HeikoKlare]

Do we? It's explicitly kept for printer in the mentioned PR: