Fix 2D light for masking feature

[Raiguri]

This fix intended for people who want to use 2D light as mask using SpriteMasking extension, while using different texture shape for 2D light instead of default radial one.

Added discard for every fragment that should be visually transparent, in both the textured and default light shaders. This makes the light's mesh only occupy the stencil buffer where it's actually visible the cone texture's real silhouette, or the circle's radius instead of the whole quad.

Before fix

Screencast_20260829_233308.webm

After

Screencast_20260829_233809.webm

[4ian]

Look at https://github.com/4ian/GDevelop/pull/9033/changes and notice what's wrong, then see how you can fix it :)
(it's fairly obvious and related to git usage, so I'm not telling it explicitly because it's important you get this right for future contributions)

[Raiguri]

Look at https://github.com/4ian/GDevelop/pull/9033/changes and notice what's wrong, then see how you can fix it :) (it's fairly obvious and related to git usage, so I'm not telling it explicitly because it's important you get this right for future contributions)

My bad, I fixed it, but for some reason semaphore few tests got timed out, how to force it to recheck it?