OutputDevice::AcquireGraphics should be protected, not public

Change-Id: I1aacc4a908798fda24de6b6f09b58dcf5d392e70
VCL: Rename ImplReleaseGraphics to ReleaseGraphics, change to protected

Change-Id: Iff4198fdd51db787461b897f2d9d8b7640dbf772