The terminal implementation uses a custom double buffering
implementation for rendering the current line. On most Platforms (Linux
and MacOS) the current implementation will always render the
double-buffered image at 100% zoom, even if the target zoom is higher.

This change adapts the implementation to directly render into the actual
control and enable native double buffering for the control instead. This
ensures that the contents are rendered at the actual target zoom,
producing sharper results on HiDPI monitors when using MacOS or Linux.

Fixes https://github.com/eclipse-platform/eclipse.platform/issues/2295

Fixes https://github.com/eclipse-platform/eclipse.platform/issues/2191
# Conflicts:
#	terminal/bundles/org.eclipse.terminal.control/src/org/eclipse/terminal/internal/textcanvas/TextLineRenderer.java