[feat] transformPage

[pixelmund]

fixes #3511

This PR implements the transformPage option on resolve.

One question that came up was, are there or will there be more properties than html on transformPage?

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[benmccann]

Thanks. Would you be able to add some docs?

I have somewhat mixed feelings about this because it doesn't seem like it should be necessary, but at the same time this is definitely a friendlier API and this is a common enough usecase that I suppose it's worth it. It looks like Rich would agree it's worth it since he filed the issue request 😄 It's too bad the Request / Response API isn't nicer, but we can't do much about that. So anyway, I guess I'm in favor of this change

[pixelmund]

Yeah ofc, i'll try to add docs once i got some free time.

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[Rich-Harris]

thank you!