Use double quotes for embed iframes

[jeremy-rifkin]

This fixes the core issue with #4541 and closes #4541, separately I'll add better diagnostics for the user for when things go wrong

[mattgodbolt]

Reading the rison spec it's a miracle this ever worked! ("single-quotes are used for quoting, but quotes can and should be left off strings when the strings are simple identifiers.") so rison itself would use ' ... though maybe we also need to URI encode? :| what if the embedded thing has any time of quote in it?

[jeremy-rifkin]

Our full links seem to work without URI encoding the whole thing and while rison uses ' I don't think it ever spits out "

[jeremy-rifkin]

Ah shoot actually it can output a " however it looks like the source part of our states is URI encoded so we don't have to worry about double quotes in source. Not sure if it's rison or something else doing that URI encoding.

[partouf]

Ah shoot actually it can output a " however it looks like the source part of our states is URI encoded so we don't have to worry about double quotes in source. Not sure if it's rison or something else doing that URI encoding.

probably LZString?