feat: support casting plain element to component via is="vue:xxx"

In Vue 3's custom elements interop, we no longer process `is` usage on
known native elements as component casting. (ref:
https://v3.vuejs.org/guide/migration/custom-elements-interop.html)
This introduced the need for `v-is`. However, since it is a directive,
its value is considered a JavaScript expression. This makes it awkward
to use (e.g. `v-is="'foo'"`) when majority of casting is non-dynamic,
and also hinders static analysis when casting to built-in Vue
components, e.g. transition-group.

This commit adds the ability to cast a native element to a Vue component
by simply adding a `vue:` prefix:

```html
<button is="vue:my-button"></button>
<ul is="vue:transition-group" tag="ul"></ul>
```

packages/compiler-core/src/parse.ts

@@ -488,7 +488,12 @@ function parseTag(
   const options = context.options
   if (!context.inVPre && !options.isCustomElement(tag)) {
     const hasVIs = props.some(
-      p => p.type === NodeTypes.DIRECTIVE && p.name === 'is'
+      p =>
+        p.name === 'is' &&
+        // v-is="xxx" (TODO: deprecate)
+        (p.type === NodeTypes.DIRECTIVE ||
+          // is="vue:xxx"
+          (p.value && p.value.content.startsWith('vue:')))
     )
     if (options.isNativeTag && !hasVIs) {
       if (!options.isNativeTag(tag)) tagType = ElementTypes.COMPONENT