Improvements to volumetric clouds shadows

[anisunity]

After getting complains froms users about the quality of the shadows, I tried improve the result a bit without any major changes.

• Added an option for the ultra 1024x1024 mode for the volumetric cloud shadows and a filtering pass to reduce the aliasing artifacts of the clouds shadow.
• Changed the number of steps to evaluate the shadow from 9 to 16.
  

Testing status
The result is improved in previously existing shadow resolutions
The result is improved with the new resolution
Some tests will need screenshot updates.

[github-actions]

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[TomasKiniulis]

Assuming Reference Images are updated and CI is passing looks good. The smaller clouds actually get shadows now and the shadows themselves look much smoother even on smaller resolutions.

Attaching test results:
Small clouds master

Small clouds PR

Larger scale clouds master 512 resolution

Larger scale clouds PR 512 resolution

Larger scale clouds PR 1024 resolution

[pierre-unity]

working well, much smoother and ability to push resolution slightly

[anisunity]

This PR has been merged in this PR for making screenshot regeneration easier #5546