fix(select): fix prop not working properly on hidden select input

[royeden]

Hello!

I've noticed that <Select /> components don't honor the required attribute properly, so this PR assigns a value attribute (same one assigned to the select element) to the input inside of <HiddenSelect />.

I wanted to add a test for this issue but I ran into the pointer-events issue that makes you skip all the current Select tests.

[netlify]

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