[widget bindings] Extract the business logic present in this crate to a new place

[BillCarsonFr]

The bindings should be a thin layer between foreign language and rust SDK. It is not a good place to put common logic for the EX apps.

E.g this should be moved to another crate/project https://github.com/matrix-org/matrix-rust-sdk/blob/b0c0e0e0c4e765d37958f30ce420701f80f1f937/bindings/matrix-sdk-ffi/src/widget.rs#L147C8-L147C45