Move bitmap functions in header, warn if calling GetBitmap() in Printer

Change-Id: Id2325822730d3d9167706c8c4118eaa3ca727195
Rename VCL's ImplInitGraphics to AcquireGraphics

Turns out, we don't try to initialize a graphics context, much less
*acquire* one. e.g. Window instances can have many frames (subwindows),
of which one some are really being used at any time so we try to
"steal" one of the graphics contexts from the frame to use ourself,
later on that frame will steal it from someone else, etc.

Change-Id: I66d5dbb7015301bc2d2be51627061c91e1f2ee5d
Rename OutputDevice::ImplGetGraphics to GetGraphics

Change-Id: I4086978f2292538c458802a7fb56c0d3826f2def