Refactor advanced.yml so that matrix strategy is moved to a parent workflow

[Blackhex]

Moves matrix strategy from advanced.yml up to a parent workflow called variants.yml calling the advanced.yml as reusable workflow. This refactor allows to run tests for other targets from the matrix. One caveat is that now the job graph does not look as nice as before.

[Blackhex]

@eukarpov Would you accept this change if individual workflows (one for each configuration) calling re-usable workflows would be used instead of the matrix? It would be less conscise and maintainable but the graph visualization would stay.

[eukarpov]

@eukarpov Would you accept this change if individual workflows (one for each configuration) calling re-usable workflows would be used instead of the matrix? It would be less conscise and maintainable but the graph visualization would stay.

My personal preference is to have good visualization. Sometimes I need to switch quickly between different PRs and custom CI runs. Good visualization helps to get quick summary about CI current progress.
For the patch series it will be hard to understand what is happening when 1k+ jobs are executed.