Add flag to reveal simpler types

[ilevkivskyi]

Something that always bothered me is that our revealed types are verbose. Sometimes they are painful to visually parse (especially for complex types). Here I propose to add a flag that for more clean/compact revealed types. With just few tweaks a typical length of a revealed type is reduced by ~half.

I know this may sometimes cause ambiguous types, but IMO such situations are very rare. We can polish this if people will like it, and maybe make the default in a distant future.

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅

[ilevkivskyi]

@JukkaL Any objections to this? This makes long revealed types much readable.

[JukkaL]

I need to think about this. One of the use cases of reveal_type is to investigate what a non-specific type name which could be defined in any number of modules actually refers to. In large codebases it's quite common to have multiple classes with the same short name. It might be better to just simplify builtins prefixes and maybe TypeVar prefixes as well, as these are unlikely to be confusing and will account for a large fraction of the noise probably.

[ilevkivskyi]

As discussed offline, we are going to:

• Split this into few smaller PRs
• Keep full names for everything non-builtin
• Make this the default behavior (no public flags, just an internal flag to simplify migrating tests)