OpenGL: OmniLight3D PCF shadow filtering not implemented

[mrjustaguy]

Godot version

4.2 beta 1

System information

Godot v4.2.beta (ee118e7) - Windows 10.0.22621 - GLES3 (Compatibility) - AMD Radeon RX 6600 (Advanced Micro Devices, Inc.; 31.0.21031.1005) - Intel(R) Core(TM) i3-10105F CPU @ 3.70GHz (8 Threads)

Issue description

PCF soft shadow support doesn't exist for Omni lights, the Shadows remain Hard.
Spot Lights and Directional Lights Soft Shadows work fine.

Steps to reproduce

Switch between Positional Soft Shadow Modes in GL renderer

Minimal reproduction project

N/A

[Calinou]

Note that PCSS-style soft shadows (variable penumbra) won't be implemented in Compatibility for performance reasons.