docs: Fix a few typos

[timgates42]

There are small typos in:

• packages/dev/proceduralTextures/readme.md
• what's new.md

Fixes:

• Should read namespace rather than namepsace.
• Should read json file rather than sjonfile.
• Should read cascaded rather than cascacaded.

Semi-automated pull request generated by
https://github.com/timgates42/meticulous/blob/master/docs/NOTE.md

[bjsplat]

Please make sure to label your PR with "bug", "new feature" or "breaking change" label(s).
To prevent this PR from going to the changelog marked it with the "skip changelog" label.

[bjsplat]

There is no need to update the "what's new.md" file. A changelog will be generated using the PR and its tags.

[bjsplat]

Snapshot stored with reference name:
refs/pull/13713/merge

Test environment:
https://babylonsnapshots.z22.web.core.windows.net/refs/pull/13713/merge/index.html

To test a playground add it to the URL, for example:

https://babylonsnapshots.z22.web.core.windows.net/refs/pull/13713/merge/index.html#WGZLGJ#4600

Links to test babylon tools with this snapshot:

https://playground.babylonjs.com/?snapshot=refs/pull/13713/merge
https://sandbox.babylonjs.com/?snapshot=refs/pull/13713/merge
https://gui.babylonjs.com/?snapshot=refs/pull/13713/merge
https://nme.babylonjs.com/?snapshot=refs/pull/13713/merge

To test the snapshot in the playground with a playground ID add it after the snapshot query string:

https://playground.babylonjs.com/?snapshot=refs/pull/13713/merge#BCU1XR#0