feat(sfc): scopeId runtime support

packages/runtime-core/src/helpers/scopeId.ts

@@ -0,0 +1,34 @@
+// SFC scoped style ID management.
+// These are only used in esm-bundler builds, but since exports cannot be
+// conditional, we can only drop inner implementations in non-bundler builds.
+
+export let currentScopeId: string | null = null
+const scopeIdStack: string[] = []
+
+export function pushScopeId(id: string) {
+  if (__BUNDLER__) {
+    scopeIdStack.push((currentScopeId = id))
+  }
+}
+
+export function popScopeId() {
+  if (__BUNDLER__) {
+    scopeIdStack.pop()
+    currentScopeId = scopeIdStack[scopeIdStack.length - 1] || null
+  }
+}
+
+export function withScopeId(id: string): <T extends Function>(fn: T) => T {
+  if (__BUNDLER__) {
+    return ((fn: Function) => {
+      return function(this: any) {
+        pushScopeId(id)
+        const res = fn.apply(this, arguments)
+        popScopeId()
+        return res
+      }
+    }) as any
+  } else {
+    return undefined as any
+  }
+}