Explicitly import distributions from torch

[fritzo]

Addresses #3332 #2550

This attempts to resolve mypy attribute undefined errors for dist.Normal and others. After these fixes, I am able to use VS Code to (1) hover over dist.Normal to read docs, and (2) detect type errors in e.g. dist.Abnormal.

1. Add --config-settings editable_mode=strict to make install which helps mypy
2. Explicitly add py.typed to package_data for setuptools<69
3. Explicitly add distributions to __all__ in pyro.distributions.torch
4. Explicitly add distributions to __all__ in pyro.distributions
5. Runs make format with the latest black

• Question: will this break anyone's installs? E.g. if torch renames a distribution, we might get an import error in pyro.distributions.
  Answer: No, since we're using both import * and try...except around explicit imports.

[ordabayevy]

I like having explicit imports. If a distribution gets renamed or a new distribution gets added maybe we can try to mitigate it by putting try/except guards to work around import errors?

[fritzo]

@ordabayevy Great, I've added try..except around the explicit imports, and also used the same implicit+explicit pattern in pyro.distributions.transforms and pyro.distributions.constraints.

[ordabayevy]

Looks great!

[akotlar]

We just ran into this; gentle suggestion to cut a patch release with this commit.