[CMake] Rework sofa_generate_package

[guparan]

This PR follows @marques-bruno work on #909

• add INCLUDE_SOURCE_DIR parameter to sofa_generate_package
• rename INCLUDE_ROOT_DIR to INCLUDE_INSTALL_DIR (avoid confusion with INCLUDE_SOURCE_DIR)

The idea is to permit this:

sofa_generate_package(
    NAME SofaSparseSolver 
    VERSION ${PROJECT_VERSION} 
    TARGETS SofaSparseSolver
    INCLUDE_SOURCE_DIR "src/SofaSparseSolver"
    INCLUDE_INSTALL_DIR "SofaSparseSolver/SofaSparseSolver"
    )

to obtain for example an install tree like this

install
    include <-- include_directories here exposes ALL module headers
        SofaBaseTopology
                header.h
        SofaSparseSolver <-- include_directories here exposes ONLY SofaSparseSolver headers
            SofaSparseSolver
                header.h
        SofaValidation
                header.h
        ...

which is needed if we want to cleanly separate SOFA include directories.

In a future PR I'd like to rework all SOFA install tree based on this INCLUDE_SOURCE_DIR + INCLUDE_INSTALL_DIR mechanism.

---

This PR:

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

Reviewers will merge only if all these checks are true.

[guparan]

TODO: add INCLUDE_INSTALL_DIR to INCLUDE_ROOT_DIR backward compat

EDIT: done!

[guparan]

[ci-build][with-scene-tests]

[damienmarchal]

Ready...go