Vulkan: LightmapGI soft shadows not reimplemented yet (unlike BakedLightmap in 3.x)

[Calinou]

See also #49935.

Godot version

4.0.dev (6d98f84)

System information

Fedora 34, GeForce GTX 1080 (NVIDIA 470.57.02)

Issue description

#50184 should be reimplemented in the GPU lightmapper on the master branch.

Constant shadow blur (Shadow Blur property) is also currently ignored, but I'm not sure if that one can be reimplemented in a lightmapper. Either way, PCSS-style shadows are arguably more important to support in a lightmapper, which is all about providing the highest quality shadows.

Steps to reproduce

• Create light nodes with their bake mode to Static (formerly All) instead of the default Dynamic (formerly Indirect Only).
• Set the lights' Size/Angular Distance to values greater than 0 (try 0.5).
• Bake lightmaps and notice that lights' shadows are still hard.

Minimal reproduction project

N/A