fix: add types to remaining exports of dev-server-core

Author: tmsns

.changeset/rare-donuts-sneeze.md

@@ -0,0 +1,5 @@
+---
+'@web/dev-server-core': patch
+---
+
+add types for remaining exports

packages/dev-server-core/package.json

@@ -21,9 +21,11 @@
  "require": "./dist/index.js"
  },
  "./dist/dom5": {
+ "types": "./dist/dom5/index.d.ts",
  "require": "./dist/dom5/index.js"
  },
  "./test-helpers": {
+ "types": "./test-helpers.d.ts",
  "import": "./test-helpers.mjs",
  "require": "./dist/test-helpers.js"
  }