[Core] Rename BaseObject to BaseComponent

[alxbilger]

This PR implements a backward-compatible transition of the core object base type from BaseObject to BaseComponent while ensuring existing code continues to compile during migration:

• Renamed core types: All forward declarations, casts, and visitor APIs operating on objects now use BaseComponent (the new type).
• Backward compatibility layer:
  • BaseObject is a deprecated alias for BaseComponent (ensures existing code compiles without changes).
  • #include <BaseObject.h> is a deprecated alias for #include <BaseComponent.h> (via header shim).
  • toBaseObject() is a deprecated alias for toBaseComponent() (forwarded internally to avoid breaking core builds).
• Build configuration: Compatibility headers are exposed to downstream consumers via include directories.
• ⚠️ Critical migration note:

This deprecation layer does not work for code using its own forward-declared BaseObject. Such code will fail with a redefinition error (e.g., BaseObject already defined). Instead of the forward declaration of BaseObject, we recommand to include <sofa/core/fwd.h>. Then, you can rename BaseObject with BaseComponent, although the deprecation layer should work.

[ci-depends-on https://github.com/sofa-framework/SofaPython3/pull/575]
[ci-depends-on https://github.com/sofa-framework/Sofa.Qt/pull/30]

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

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By submitting this pull request, I acknowledge that
I have read, understand, and agree SOFA Developer Certificate of Origin (DCO).

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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).

[fredroy]

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

[sofabot]

[ci-depends-on] detected during build #5.

All dependencies are merged/closed. Congrats! 👍

[sofabot]

[ci-depends-on] detected during build #6.

To unlock the merge button, you must

• Merge or close include sofa/core/fwd.h instead of the forward declaration Sofa.Qt#30
  For this build, the following CMake flags will be set
  -DSOFA_QT_GIT_REPOSITORY='https://github.com/sofa-framework/Sofa.Qt'
  -DSOFA_QT_GIT_TAG='18eb1108fc75996ebcf748711cd4990b6dabb54a'

[sofabot]

[ci-depends-on] detected during build #7.

To unlock the merge button, you must

• Merge or close include sofa/core/fwd.h instead of the forward declaration Sofa.Qt#30
  For this build, the following CMake flags will be set
  -DSOFA_QT_GIT_REPOSITORY='https://github.com/sofa-framework/Sofa.Qt'
  -DSOFA_QT_GIT_TAG='18eb1108fc75996ebcf748711cd4990b6dabb54a'

[sofabot]

[ci-depends-on] detected during build #8.

To unlock the merge button, you must

• Merge or close include sofa/core/fwd.h instead of the forward declaration Sofa.Qt#30
  For this build, the following CMake flags will be set
  -DSOFA_QT_GIT_REPOSITORY='https://github.com/sofa-framework/Sofa.Qt'
  -DSOFA_QT_GIT_TAG='a2435ca64136ea14f8d076f9f6a59678080860b2'