Misc tests cleanup

[Simn]

Our misc tests are a huge mess, so let's try to clean that up.

The directory structure should be like this for all targets:

misc
    eval
        projects
        other-target-specific-tests

The projects directory remains the one that is auto-explored by the runner. To that end, the runner now changes its cwd to its first CLI argument, so we can do --run Main eval to run the eval tests.

I've also moved the toplevel projects directory to eval/projects and updated the CI references to it. Here's what we need to do now:

1. Also add a "cross" directory for tests that are run on multiple targets, following the same structure as above.
2. Delete all the current target/run.hxml we no longer need.
3. Go through the non-target sub-directories in tests/misc and move them to where they should be by inspecting what their HXMLs run.
4. Update all references in tests/runci accordingly.
5. Go through all projects in eval/projects and move the ones that are actually running other targets.
6. Update all references in tests/runci accordingly.
7. Test if it works and make adjustments until it does.

[Simn]

@copilot There's your mission! I recommend making the first commit after step 4 and another one after step 6. Note that CI is currently already broken for eval and JS (and maybe others that haven't run yet), which may or may not be addressed by the changes here.

[Copilot]

@Simn I've opened a new pull request, #12760, to work on those changes. Once the pull request is ready, I'll request review from you.