[DRAFT] Add packaging.filenames API

[di]

Draft PR so @woodruffw can contribute here. I'm also fine w/ early reviews/comments and bikeshedding on the API names.

Eventually, this should resolve:

• Utility functions to compose file distribution names #408
• Ambiguous version parsing in parse_sdist_filename #527
• Bug: parse_wheel_filename permits non-normalized versions. #873
• Bug: parse_wheel_filenames accepts wheel filenames with unsorted compressed tag sets #909

Some todos:

• Enforce compressed tag set ordering
• General alignment w/ error messages vs. what PyPI uses
• Documentation
• Deprecation of parse_wheel_filename and parse_sdist_filename

[notatallshaw]

Pip will almost always use strict=False, which is spec complaint:

Tools consuming wheels must be prepared to accept . (FULL STOP) and uppercase letters, however, as these were allowed by an earlier version of this specification.

So we do not want to call canonicalize_name on every instantiation of WheelFilename, perhaps something like:

    if not strict:
        self._name = None
    else:
        # Check that the name is normalized
        self._name = canonicalize_name(name).replace("-", "_")
        if strict and self.original_name != self._name:
            raise InvalidWheelFilename(
                f"Invalid filename (non-normalized project name {name!r}): {filename!r}"
            )
    ...

    @property
    def name(self) -> NormalizedName:
        if self._name is None:
            self._name = canonicalize_name(name).replace("-", "_")
        return self._name

[notatallshaw]

Big resolutions in pip involve scanning hundreds of thousands of distributions, can all the classes please use __slots__.