Support for unordered_pointwise

We are extensively using googletest-rust in our Google-internal Android repo. I am wondering whether you could add support for something like unordered_pointwise? I attempted to wrap `pointwise` with `unordered_elements_are`, but that appears to expect a literal list of matchers, whereas `pointwise` returns a single matcher for the entire container.

Start by reading the existing `pointwise` and `unordered_elements_are` matcher APIs and their tests. Determine how an unordered pointwise matcher should compose those behaviors, then add focused coverage showing unordered matching and the expected failure behavior; done means the proposed API works without requiring a literal matcher list.

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