Fix memory leaks

[RaananW]

See https://forum.babylonjs.com/t/slidr3d-causes-a-memory-leak/35597

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[sebavan]

I approved and merged but just noticed there are no dispose on the textures @RaananW ?

[RaananW]

I approved and merged but just noticed there are no dispose on the textures @RaananW ?

Addressed in #13235
Thanks!