Major version 3.0.0 about pdepend

[AJenbo]

I made PRs for dropping the rest of the unsupported PHP versions. In total that will get us to 5000 lines removed since 2.x.

I also made one for removing things marked as deprecated, except for two functions that are still used internally.

Settling on a code styles and which tool to use for it should be the next step I think. Having that cleared up will make cleaning up syntax a lot easier.

I think it could be good to have 3.x out by the time PHP 8.4 arrives (November 2024).

I would also like to get the project to pass PHPStan level 9 by then, I think it's a doable target and we are a bit more free as to how to approach it during the 3.x cycle.

[ravage84]

We set up some pages for the new major version 3.0 in the repo wiki:

• 3.0-Goals
• 3.0-Ideas
• 3.0-Roadmap