Custom attributes and single quotes aren't converted properly

`data-sheets-userformat='{"2":5059,"3":[null,0],"4":[null,2,15389148],"9":1,"10":1,"11":4,"12":0,"15":"Calibri"}'`
and
`style='font-family: "Times New Roman"'`
are converted into:
`data-sheets-userformat="{"2":5059,"3":[null,0],"4":[null,2,15389148],"9":1,"10":1,"11":4,"12":0,"15":"Calibri"}"`
and
`style="font-family: "Times New Roman""`

The single quotes `'` are converted into double quotes `"`, which break the html.

Reproduce the conversion using the data-sheets-userformat and style examples in the issue, then trace the HTML attribute parsing or serialization entry point that changes single quotes. Done means both attributes remain valid HTML with their embedded JSON and quoted font family intact, and regression coverage verifies these examples.

Written by the indexing model from the issue text.