When I execute a Format Document command on a Vue Component.vue file VSCode replace all single quoted string with double quoted string.
Format Document
In my specific case
From the vuejs/vetur issue page https://github.com/vuejs/vetur/issues/986# This solution worked for me.
In VSCodes settings.json file add this entry
settings.json
"vetur.format.defaultFormatterOptions": { "prettier": { "singleQuote": true } },