Build demo apps with a package built from workspace

[NorbertKlockiewicz]

Problem description

Right now demo apps are built with a package fetched from npm. It prevents us from running ci actions to check if current changes aren't causing build issues.

Proposed solution

Build demo apps with a package built from current workspace.

Alternative solutions

No response

Benefits to React Native ExecuTorch

CI will be somehow useful, also newest changes can be easily checked, and there's no need to build package by hand when developing

Additional context

No response