Add `partial` option

minimatch has a partial option that seems to do a partial match. This is great for optimizations in path traversal libraries. As per minimatch's docs:

partial

Compare a partial path to a pattern. As long as the parts of the path that
are present are not contradicted by the pattern, it will be treated as a
match. This is useful in applications where you're walking through a
folder structure, and don't yet have the full path, but want to ensure that
you do not walk down paths that can never be a match.

For example,

minimatch('/a/b', '/a/*/c/d', { partial: true }) // true, might be /a/b/c/d
minimatch('/a/b', '/**/d', { partial: true }) // true, might be /a/b/.../d
minimatch('/x/y/z', '/a/**/z', { partial: true }) // false, because x !== a

I am building a library that would greatly benefit from this functionality, but I also would rather not switch to minimatch as I greatly value picomatch's advantages in terms of performance. It also seems like I'm not the first one to suggest this, as someone also opened a feature request in micromatch (micromatch/micromatch#276).

Many existing libraries that make use of picomatch (that currently implement this behavior themselves) would also benefit from this, such as fast-glob: https://github.com/mrmlnc/fast-glob/blob/096a5b620f4224eb692bd8ff2c8de0e634e50d8e/src/providers/matchers/partial.ts

Start with the minimatch partial option description and the three examples in the issue, then compare the existing behavior with fast-glob's referenced src/providers/matchers/partial.ts. Done means picomatch supports partial paths without contradicting patterns, including the positive and negative cases described, with matching tests added in the repository's existing test structure.