Migrate from tsc to rollup for the build process (#38)

this PR migrates the build chain from tsc to rollup, as part of the changes discovered in the investigation from this [PR](yext/chat-ui-react#38): 

J=CLIP-556
TEST=manual

see that all unit tests and the two test site still works as expected
published an alpha version `[0.7.0-alpha.38.2](https://www.npmjs.com/package/@yext/chat-headless/v/0.7.0-alpha.38.2)` of headless and alpha version `[0.6.0-alpha.38.3](https://www.npmjs.com/package/@yext/chat-headless-react/v/0.6.0-alpha.38.3)` of headless-react, and see that it still works as expected in vite/pagesjs and sonic/alpha.

Will publish v0.7.0 of headless once merged. Then update headless-react dep in a separate PR to publish 0.6.0

.eslintrc.js

@@ -8,6 +8,7 @@ module.exports = {
     "**/index.ts",
     "**/build",
     "**/coverage",
+    "rollup.config.mjs",
     "*.d.ts",
   ],
   parserOptions: {

apps/test-site/package.json

@@ -14,9 +14,9 @@
     "web-vitals": "^2.1.4"
   },
   "scripts": {
-    "start": "craco start",
-    "build": "craco build",
-    "test": "craco test"
+    "start": "react-scripts start",
+    "build": "react-scripts build",
+    "test": "react-scripts test"
   },
   "browserslist": {
     "production": [
@@ -29,8 +29,5 @@
       "last 1 firefox version",
       "last 1 safari version"
     ]
-  },
-  "devDependencies": {
-    "@craco/craco": "^7.1.0"
   }
 }