chore(build): set an explicit rootDir for declaration output (#540)

@rollup/plugin-typescript 12 no longer sets `rootDir` itself, and
TypeScript 6 no longer infers the common source directory (TS5011).
This repo is still on plugin 11, so the emitted layout is currently
correct — but without an explicit `rootDir` the next plugin bump would
move the entry declarations to `dist/<fmt>/src/index.d.ts` while
`package.json` keeps pointing `types` at `dist/<fmt>/index.d.ts`.

That is exactly what broke the pro packages: @coreui/vue-pro from
5.20.0 (coreui/coreui-pro#704) and @coreui/react-pro from 5.27.0, in
both cases with TS7016 on every import for every TypeScript consumer.

Author: mrholek

packages/coreui-react/tsconfig.json

@@ -1,4 +1,7 @@
 {
   "extends": "../../tsconfig",
+  "compilerOptions": {
+    "rootDir": "src"
+  },
   "include": ["src/**/*"]
 }