Rename GetGraphics to AcquireGraphics

Currently there are a number of classes that have a function called
GetGraphics(). It returns a SalGraphics instance if one is available
for the sole use of the caller. Some variants keep a pool of available
SalGraphics and return one not currently in use by anyone, creating
extra ones on demand, sometimes up to a set limit and returning NULL
on reaching that limit of simultaneously in use SalGraphics.

This is confusing. What is really happening from the perspective of the calling
is that is that we are attempting to *acquire* ownership of a SalGraphics
instance.

Therefore, rename GetGraphics to AcquireGraphics() which returns a handle to a
SalGraphics if we can acquire a free graphics instance, and NULL if we cannot,
which makes it cleared that ReleaseGraphics should be called on the result
of AcquireGraphics.

The classes that were changed to include the new acquire function are:

* SalFrame
* SalVirtualDevice
* SalInfoPrinter
* PspSalInfoPrinter
* X11SalFrame
* X11SalVirtualDevice
* GtkSalFrame
* KDESalFrame
* TDESalFrame
* WinSalFrame
* WinSalInfoPrinter
* WinSalVirtualDevice
* SvpSalFrame
* SvpSalVirtualDevice
* AquaSalFrame
* AquaSalInfoPrinter
* AquaSalVirtualDevice

Change-Id: Ic39c08a4bcaf665ae08ba2808cd03b0e80790c46
Reviewed-on: https://gerrit.libreoffice.org/8070
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>