[WIP] Refactor xtask and test workflow into CI workflows and actions

[syl20bnr]

This PR refactor the xtask crate to usethe new crates xtask-common and xtask-macros from the xtask repository.

It also refactors the test.yml into the ci.yml files using composite actions to setup rust and OSes in the actions directory. The big matrix have been split into several jobs. Now each OS has its own jobs with smaller matrices. Checks and documentation have their own jobs too.

It introduces a new convention which is that all the integration tests file names (the tests that are in a tests directory) must start with test_ prefix.