Remove visiblity and lookup deprecation - Take 2

[JinShil]

This is another try at #7241. It will also resolve Issue 19471.

Much credit to @MartinNowak and @wilzbach. Sorry, I didn't know how to rebase the original PR.

There are a couple of outstanding issues with this PR, and it will need help from reviewers:

1. test/compilable/test15177.d does not pass. It's generating code with __traits(allmembers) and that's bringing in symbols that aren't visible. I don't know what the correct behavior is.
2. I'm not terribly happy with the kind of error messages being emitted.

My suggestion to reviewers: Look at the test cases and see if the output makes sense.

cc @RazvanN7, @Geod24

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[jacob-carlborg]

test/compilable/test15177.d does not pass. It's generating code with __traits(allmembers) and that's bringing in symbols that aren't visible. I don't know what the correct behavior is.

Hmm, the test15117a module is imported and all symbols are public in that module. To me it looks like it should work.

Not sure if this is related but __traits(allMembers) (and possible other __traits) need to be able to read private symbols, we have agreed on that. Otherwise you'll get an error when iterating the result of __traits(allMembers) when it contains private symbols, even tough you're not trying to access them. It's not even possible to check if a symbol is private and skip it.

[JinShil]

I'm really sorry folks. I spent the whole day on this, and the rabbit hole just keeps getting deeper. I can't afford the time to follow it right now; I thought it would be just a few hours. Maybe another time. I'm really sorry. I tried.