Allow returning memoryview in StreamingResponse

[bschoenmaeckers]

Summary

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.

[adriangb]

Makes sense to me!

[Kludex]

What's the use case? To create the memoryview you need bytes or bytearray anyway...

[bschoenmaeckers]

Memoryview allows you to efficiently return a slice of the original bytes value without copying. This is especially convenient when you want to strip some prefix or header of some value in memory you don’t control.

[adriangb]

Yup I'd say the use cases are varied, it allows moving around bytes with zero copying.

[Kludex]

This is a PR without description, and there's a single discussion that mentioned this feature request (that is 4 years old) without reactions.

Also, this can be easily done by overriding the stream_response method. And that's what we've always recommended.

[adriangb]

Feel free to revert it if you don’t agree. To me it made sense and was simple.