Add const_prop_pass inside to_edge

[tarun292]

🐛 Describe the bug

Currently we're not running a const prop pass inside to_edge and many users are manually invoking this pass inside their workflows. We should just run this inside to_edge by default.

Versions

cc @JacobSzwejbka @angelayi

[mergennachin]

And/or run directly inside the new executorch.export API?

[tarun292]

@mergennachin i think we'd still want to run it inside to_edge because for users that don't want to leverage the executorch.export API we'll still want them to benefit from this.