Time Factor for crowd agents update

[CedricGuillemet]

Follow up https://forum.babylonjs.com/t/possible-to-pause-recastjs-crowd-navigation/33025/7
And add a little twist.
Instead of just pausing a sim, it's possible to change the time factor. So a pause is possible, and even a progressive one.

[azure-pipelines]

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.

[azure-pipelines]

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