Backport dataurl sourcemap support

[abstraktor]

See #1914 and #1915

I am unsure if this is a correct branch for future minor versions. Move it around as you like.

Have a great day,
Bastian

[CLAassistant]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[Shtilianova]

Hello @abstraktor ,
This pull request and #1914 and connected into our internal one 1870087779.The status of the issue will be updated here in GitHub.
Regards, Diana

[matz3]

Thank you for your efforts! Unfortunately we are not accepting this PR. Please see my comment in #1914.