Add IJ1Helper#shiftKeyDown()
Add IJ1Helper#shiftKeyDown()

This adds a simple delegator to ask ImageJ 1.x whether it thinks that
the Shift key is held down.

Signed-off-by: Johannes Schindelin <53fb8db7833fca1e1746dd8592f61048d350f64c@gmx.de>

imagej/imagej-legacy,imagej/imagej-legacy,imagej/imagej-legacy,imagej/imagej-legacy