Issues porting to Monocle EPD platform

[John Neffenger]

While porting OpenJFX to devices with an electronic paper display, I 
resolved three issues in the graphics module that I thought I should 
pass along. The following merge request on GitLab lists the issues and 
my minor changes. See the Commits and Changes tabs in the middle of the 
page for details.

WIP: Patches to OpenJFX
https://gitlab.com/openjfxepd/jfxpatch/merge_requests/1

Did I understand the code correctly? I would appreciate any feedback.

As a brief summary, the first issue, "QuantumRenderer modifies buffer in 
use by JavaFX Application Thread," may be of general interest because it 
occurs on the Monocle Headless and VNC platforms.

The second issue, "zForce touchscreen input device fails when closed and 
immediately reopened," might affect only my platform, or maybe just the 
older Linux kernel and device driver I'm forced to use, but I couldn't 
find a good workaround without duplicating the entire LinuxInputDevice 
class.

The third issue, "Get two bytes for the Linux input event type, not 
four," doesn't seem to cause any problems, but may still be worth fixing.

Thank you,
John