[Feature Request] MockedProvider can pass down props to child component

[miachenmtl]

Allow MockedProvider to accept a props object as prop, and to inject the key/values of the props object as props for the child component. This is useful for testing components using enzyme's setProps method, which only runs on the root node.

Checklist:

• If this PR is a new feature, please reference an issue where a consensus about the design was reached (not necessary for small changes)
• Make sure all of the significant new logic is covered by tests
• If this was a change that affects the external API used in GitHunt-React, update GitHunt-React and post a link to the PR in the discussion.

[apollo-cla]

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[hwillson]

Thanks for this @miachenmtl I've changed props to childProps for a bit of extra clarity, but other than that we're all set here. LGTM - thanks!