fix: rawContent was not correctly cloned (hence undefined)

[e-krebs]

Summary

Fixing an error made in #6544, where using Object.create(content) resulted in rawContent always being an empty object and the final _rawContent property always being undefined.
Now using a custom method to smartly clone content without the results property, which behaves correctly.

This approach avoids the need to delete the results property as it "just" creates a new object without it in the first place.
This result in a more performant approach than using the existing merge util + deleting the results property afterward.

Result

_rawContent as retrieved in the below example is now not always undefined anymore.

const { results: { _rawContent } } = useInstantSearch();

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