[Visual] Scene center and radius are not longer cached

[alxbilger]

This PR removes the cache mechanism around the scene center and radius in the BaseCamera class.

Removed:

• Data member sceneCenter and sceneRadius are removed. This is breaking for derived class using them.

Added:

• Methods to get the scene center and radius when needed.

Changes:

• The cached scene center and radius are replaced by direct calls to the newly added methods.

Effects:

• If fixes a bug producing nans in the projection matrix of the camera. The cached value sceneCenter was used, but it was not already computed and cached. Therefore, the default value was used (likely zero). The default value was then used to compute Znear and Zfar, resulting both to be set to zero. At some point there is a division by (currentZFar - currentZNear), leading to a nan.

Before:

After:

Note that I don't understand why having nan is not problematic. I am not sure neither if having valid values helps.

I took the opportunity to add easy constness to some methods.

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Reviewers will merge this pull-request only if

• it builds with SUCCESS for all platforms on the CI.
• it does not generate new warnings.
• it does not generate new unit test failures.
• it does not generate new scene test failures.
• it does not break API compatibility.
• it is more than 1 week old (or has fast-merge label).