[analyzer] Moved the whole SMT API to a single file. NFC.

[mikhail.ramalho]

Summary

There is no advantage in having them in separate files, I doubt some will ever use them separately.

This also makes it easier to move the API to LLVM.

[george.karpenkov]

The advantage is it's easier to find stuff with a 1-1 correspondence between class names and files.
Thus for this change I see a disadvantage and no clear advantages.

[mikhail.ramalho]

In D54977#1310620, @george.karpenkov wrote:

The advantage is it's easier to find stuff with a 1-1 correspondence between class names and files.
Thus for this change I see a disadvantage and no clear advantages.

I agree that having separate files helps but I'll send the other backends in the future, adding even more files.

I was trying to reduce the clutter. Do you think I should put everything in a separate directory instead?

[NoQ]

I don't mind, it's entirely a matter of taste, as far as i understand. Please feel free to make it as comfortable for yourself as possible.

Generally people are annoyed a bit by this sort of commits because when you move things around git blames get screwed.