SelectPolygon: preserve first-pixel marker size in pixels on zoom

[woutdenolf]

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PR summary

Marker of the first point in a polygon stays the same size on zooming. Closing the polygon is done when clicking on the marker.

import sys

from silx.gui import qt
from silx.gui.plot import Plot1D

app = qt.QApplication(sys.argv)

plot = Plot1D()

plot.addCurve([0, 100], [0, 100], legend="diag")

plot.setLimits(0, 100, 0, 100)
plot.show()

plot.setInteractiveMode("draw", shape="polygon")

sys.exit(app.exec())

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[payno]

From what I saw only the polygon ROI needs a marker to 'close the loop' right ?

[payno]

Thanks 👍
Fine with it except if the square marker is used for other ROI but It doesn't looks so.

[payno]

I saw a typo on the (already existing) doc. I allowed myself to fix it and embed it with this PR (e0c3d5b)