MultiEffect API review

Have API review for MultiEffect as it will be new in Qt 6.5.

Here are few things to consider:

1. Are "maskThresholdLow" and "maskThresholdUp" named correctly? If I think pairs, "upper" and "lower" match but "up" and "low" not so much. Instead "low" & "high" or "up" & "down" also match. What are correct API terms for threshold and spread? GE ThresholdMask don't have this issue as it only supports single threshold & spread https://doc-snapshots.qt.io/qt6-dev/qml-qt5compat-graphicaleffects-thresholdmask.html
2. Is "colorize" correct naming for this effect? Implementation of this colorize does not match to GE colorize with hue, lightness & saturation (https://doc.qt.io/qt-5/qml-qtgraphicaleffects-colorize.html). Instead it matches to GE "ColorOverlay" (https://doc.qt.io/qt-5/qml-qtgraphicaleffects-coloroverlay.html) with the exception that alpha has separate "colorize" property for easy usage. I probably selected colorize originally as "colorOverlayColor" property name felt a bit long. But I don't think there is clear definition for colorize effect, e.g. as an comparison, Blender colorize seems similar to color overlay (https://docs.blender.org/manual/en/latest/grease_pencil/visual_effects/colorize.html).
3. Should mask default to show/hide masking or static mask? Current defaults for threshold and spread (0, 0, 1, 0) are optimal for cases where user animates hide/show with the mask. In this case user sets some spread and then animates either lower threshold to 1.0 or higher to 0.0. Alternative defaults could be made to match OpacityMask (0.5, 1, 1, 0) where mask source would mask correctly with the image alpha.
4. Should "autoPaddingEnabled" default to true of false? Currently defaults to true, so items which user wants to expand when blurred as well as actually seeing the shadow by defaut. But when use case is e.g. blurring the whole background, user needs to remember to turn this off for optimal performance as item grows outside the viewed area. This autopadding is somewhat similar to FastBlur "transparentBorder" which defaults to false, https://doc.qt.io/qt-6/qml-qt5compat-graphicaleffects-fastblur.html#transparentBorder-prop
5. See ticket QTBUG-109555. Should "hasProxySource" be renamed to "useProxySource", and now or later add WRITE method for it to force source creation?