better way to resolve `Phase::Emergency` via governance (#10663)

* better way to resolve Phase::Emergency via governance

* Update frame/election-provider-multi-phase/src/lib.rs

Co-authored-by: Zeke Mostov <[email protected]>

* review grumbles

* Update frame/election-provider-support/src/onchain.rs

Co-authored-by: Shawn Tabrizi <[email protected]>

* revert usize -> u32

Co-authored-by: Zeke Mostov <[email protected]>
Co-authored-by: Shawn Tabrizi <[email protected]>