PR: Provide icon size when creating an `IconWidget`

[StSav012]

I suggest adding a size keyword-only argument to the constructor of IconWidget to avoid extra setIconSize and update calls.

This way,

icon_widget: qta.IconWidget = qta.IconWidget('mdi.web', color='blue')
icon_widget.setIconSize(QtCore.QSize(32, 32))
icon_widget.update()

turns into

icon_widget: qta.IconWidget = qta.IconWidget('mdi.web', color='blue', size=QtCore.QSize(32, 32))

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And I fixed a couple of typos in the docstring of the class.