[IMP] runtime/utils: export htmlEscape and add tests

markup tag function requires markup awareness to determine whether a
given parameter should be escaped or not.

This implies that pre-escaped content should be properly marked'ed up to
avoid double escaping. Having to manually wrap all calls to escape
with markup is cumbersome and prone to issues (on top of having to be
validated by the security team for no reason).

This commit introduces a markup-aware escape function to resolve those
issues.

src/runtime/index.ts

@@ -41,7 +41,7 @@ export { useComponent, useState } from "./component_node";
 export { status } from "./status";
 export { reactive, markRaw, toRaw } from "./reactivity";
 export { useEffect, useEnv, useExternalListener, useRef, useChildSubEnv, useSubEnv } from "./hooks";
-export { batched, EventBus, whenReady, loadFile, markup } from "./utils";
+export { batched, EventBus, htmlEscape, whenReady, loadFile, markup } from "./utils";
 export {
   onWillStart,
   onMounted,