feat(store): return setImportMap and add merge parameter

[wangcch]

const store = useStore();

store.setImportMap({}, true)

getImportMap(): ImportMap
setImportMap(map: ImportMap, merge?: boolean): void

[vercel]

@wangcch is attempting to deploy a commit to the vuejs Team on Vercel.

A member of the Team first needs to authorize it.

[edison1105]

LGTM

[pkg-pr-new]

Open in Stackblitz

npm i https://pkg.pr.new/@vue/repl@314

commit: 9f53bd1