Reduce performance overhead of directional shadow support

[tomas7770]

Description

The newly added support for directional lights casting shadows has resulted in a drastic performance loss (about half in some cases), even when shadows aren't enabled, due to changes in the deferred shading.

Expected behaviour

When shadows are disabled, the performance impact of merely supporting them should be minimal.

[RiscadoA]

Damn we really need to improve this on 0.5 💀 samples become outright unplayable on my laptop

[tomas7770]

Lowering the max number of cascades and/or removing the directional light greatly improves performance on my laptop. Adding more directional lights worsens it. Maybe the bottleneck is passing the cascade matrices to the GPU?