Correctly find dependencies when installed

[jcortial-safran]

Use find_dependency instead of find_package in installed CMake config to correctly propagate QUIET and REQUIRED flags to users.

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

:exclamation: No coverage uploaded for pull request base (master@bae2c83). Click here to learn what that means.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #261 +/- ## ========================================= Coverage ? 43.98% ========================================= Files ? 179 Lines ? 54124 Branches ? 10252 ========================================= Hits ? 23805 Misses ? 22599 Partials ? 7720 ```

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[jcortial-safran]

The change had the unfortunate side-effect to make the CMake configuration fail whenever either SCOTCH or VTK are absent, even if these packages were not used when building Mmg. So it is a significant regression compared to the previous state.

Sorry for that, I should have tested more throughly. I will submit a fix as a new PR.

[Algiane]

Thanks for the feedback.

I haven't particularly tested the PR as the integration tests didn't fail but the config files generated by CMake are not tested 😅 .