fix(language-service): expose package.json for vscode extension resolution (#48678)

The VSCode extension looks for `@angular/language-service/package.json`
using `require`. This currently breaks as of the ESM changes because
we introduced the `exports` field but did not expose the `package.json`.

This commit fixes it.

Co-authored-By: Andrew Scott <atscott@google.com>
Co-authored-By: Dylan Hunn <dylhunn@gmail.com>

PR Close #48678

packages/language-service/package.json

@@ -14,6 +14,9 @@
       "types": "./index.d.ts",
       "default": "./index.js"
     },
+    "./package.json": {
+      "default": "./package.json"
+    },
     "./api": {
       "types": "./api.d.ts",
       "default": "./api_bundle.js"