Mask2D: sprite-easy masking for Godot 4

Add a Mask2D node under any Sprite2D, Polygon2D, Label or Control, pick a shape, and move, rotate or animate it like a sprite. Everything nested underneath is masked too.

Features: reveal or cut holes (invert); rectangle, ellipse, rounded rectangle or any texture (alpha or luminance); soft edges, threshold and softness for dissolves and wipes; up to 4 masks per node, combined automatically; mask nodes anywhere in the tree, so mask and content move independently; script API get_coverage_at() for click tests on visible areas; live editor preview with no SubViewports, no CanvasGroups, no shader code and no changes to your scene files; one lightweight shader, tested with Compatibility and Forward+ on Godot 4.7.

Solves godot-proposals #4282, open since 2022 with 300+ upvotes. Try the free Lite edition first (rectangle, ellipse, texture, invert, 1 mask per node).

Includes the addon, a demo scene with 8 examples, README and changelog. License: use in any of your own projects, commercial or not; resale or redistribution of the addon itself is not allowed.