feat(portal): SSR support for multi portal shared target

packages/server-renderer/src/helpers/ssrRenderPortal.ts

@@ -2,19 +2,24 @@ import { ComponentInternalInstance, ssrContextKey } from 'vue'
 import { SSRContext, createBuffer, PushFn } from '../renderToString'
 
 export function ssrRenderPortal(
+  parentPush: PushFn,
   contentRenderFn: (push: PushFn) => void,
   target: string,
   parentComponent: ComponentInternalInstance
 ) {
+  parentPush('<!--portal-->')
   const { getBuffer, push } = createBuffer()
-
   contentRenderFn(push)
+  push(`<!---->`) // portal end anchor
 
   const context = parentComponent.appContext.provides[
     ssrContextKey as any
   ] as SSRContext
   const portalBuffers =
     context.__portalBuffers || (context.__portalBuffers = {})
-
-  portalBuffers[target] = getBuffer()
+  if (portalBuffers[target]) {
+    portalBuffers[target].push(getBuffer())
+  } else {
+    portalBuffers[target] = [getBuffer()]
+  }
 }