Decouples light-sync state from chain spec (#9491)

* Decouples light-sync state from chain spec

This decouples the light-sync state from chain spec. First, the
light-sync state currently only works with BABE+Grandpa, so not
all *Substrate* based chains can use this feature. The next problem was
also that this pulled the `sc-consensus-babe` and `sc-finality-grandpa`
crate into `sc-chain-spec`.

If a chain now wants to support the light-sync state, it needs to add
the `LightSyncStateExtension` to the chain spec as an extension. This is
documented in the crate level docs of `sc-sync-state-rpc`. If this
extension is not available, `SyncStateRpc` fails at initialization.

* Fix compilation for browser

* Fmt