chore(api): add `package.json` to the `exports` field (#1807)

* chore(api): add `package.json` to the `exports` field

* move exports to package.json

.changes/api-export-package-json.md

@@ -0,0 +1,5 @@
+---
+"api": patch
+---
+
+Adds `package.json` to the `exports` object.

tooling/api/package.json

@@ -7,6 +7,9 @@
     "type": "opencollective",
     "url": "https://opencollective.com/tauri"
   },
+  "exports": {
+    "./package.json": "./package.json"
+  },
   "scripts": {
     "build": "rimraf ./dist && rollup -c --silent && node ./scripts/after-build.cjs",
     "npm-pack": "yarn build && cd ./dist && npm pack",