Properly break exception chain in `importlib.metadata.Distribution.from_name()`

[bswck]

Bug report

Bug description:

>>> import importlib.metadata
>>> importlib.metadata.distribution("-")
Traceback (most recent call last):
  File ".\Lib\importlib\metadata\__init__.py", line 458, in from_name
    return next(iter(cls._prefer_valid(cls.discover(name=name))))
StopIteration

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<python-input-1>", line 1, in <module>
    importlib.metadata.distribution("-")
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^
  File ".\Lib\importlib\metadata\__init__.py", line 1032, in distribution
    return Distribution.from_name(distribution_name)
           ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^
  File ".\Lib\importlib\metadata\__init__.py", line 460, in from_name
    raise PackageNotFoundError(name)
importlib.metadata.PackageNotFoundError: No package metadata was found for -

This message is somewhat incorrect and can be much shorter. PackageNotFoundError is the interesting exception, while StopIteration is just an implementation detail, so there's no need to include the latter.

Instead, I'd expect:

>>> import importlib.metadata
>>> importlib.metadata.distribution("-")
Traceback (most recent call last):
  File "<python-input-1>", line 1, in <module>
    importlib.metadata.distribution("-")
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^
  File ".\Lib\importlib\metadata\__init__.py", line 1032, in distribution
    return Distribution.from_name(distribution_name)
           ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^
  File ".\Lib\importlib\metadata\__init__.py", line 460, in from_name
    raise PackageNotFoundError(name) from None
importlib.metadata.PackageNotFoundError: No package metadata was found for -

It contains everything necessary for this specific traceback.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Windows

Linked PRs

• gh-140141: Properly break exception chain in importlib.metadata.Distribution.from_name #140142