[Core] Introduction of TopologyAccessor

[alxbilger]

For a unification of all the component accessing a BaseMeshTopology.

It has been applied to only a few components, but it has to be generalized (in another PR).

[with-all-tests]

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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).

[alxbilger]

[ci-build][with-all-tests]