Handle partial encoding situation by firebase storage image URLs

[gabrielsze]

Hi team, thanks for the great library thus far - this is one of my first few times contributing and submitting a PR, so do bear with me and let me know how I can improve :)

This is related to https://github.com/nuxt/image/issues/435, where ipx is not handling firebase storage image weird URL structure, for example

https://firebasestorage.googleapis.com/v0/b/amber-prod.appspot.com/o/images%2Fwatch-dogs-2-sitara-dhawan-render-3-woman-holding-black-and-blue-tumbler-png-clipart_1593206709107?alt=media&token=a42c3f00-89d2-4ce1-9893-da0a5c039f6e

• We can see the first half is firebasestorage.googleapis.com/v0/b/amber-prod.appspot.com/o/ is decoded, while the second half is a quite a mess and mixture of both
• For firebase image storage URLs to work, their string must be treated as opaque URLs and cannot be further decoded/encoded. (https://stackoverflow.com/questions/66419381/get-non-percent-encoded-url-from-firebase-storage)

There are several steps to handle a firebase storage image URL.

• Once req.url is handled, they automatically encode the second part of the URL again (resulting in some double encoding). To circumvent this, we have to decode the back part once.
• Since everything in the second half of the URL is decoded, we lose the original %2F that represents /, which are the forward slashes in the firebase storage image URL.
• Hence, we then need to replace the forward slashes in the second half of the URL to be the %2F as per the original firebase storage image URL since they are not supposed to be decoded.
• Finally, we don't decode it as per usual URLs since the final string is the absolute/accurate URL we need.

Explanation is also included in the code for reference and understanding.

[pi0]

Thanks for spending time and working on this pull request @gabrielsze but i don't think it is the best idea to include firebase encoding conditions inside ipx. Let's track it in https://github.com/nuxt/image/issues/435 i will do my best to investigate and help.