CI: Unify build jobs with reusable workflows

[guihkx]

Instead of having individual workflow runs for every git operation, we can instead make them 'reusable' and then bundle all of them into a single, central workflow (which we will call CI).

Having them unified into a single workflow like that has several advantages:

• Build jobs will only run if the Code Linting workflow passes first: Previously, build jobs would run in parallel with the linting workflow, which is probably undesired.

• Build artifacts for every OS will be all in the same job.

• This makes release automation much easier, which I intend to do next.

Finally, if for some reason we want to run a specific workflow individually (instead of running of all them), I've kept the workflow_dispatch option in each workflow, so we can always dispatch them manually.

[guihkx]

This setup looks kinda convoluted if you view it from the Checks tab in this pull request, but if you go to the Actions page instead, it looks much better, IMO.

Anyway, let me know your thoughts.

[nuttyartist]

I like it too! Looks much better this way, when everything is in one place.

[guihkx]

Awesome! :smile:

[guihkx]

I just pushed a commit (https://github.com/nuttyartist/notes/commit/5b76489d2f8bb5d4feb782e7049645e7676c8572) directly into master to address the failing macOS build, which was caused by the lack of access to GitHub Secrets.