Bandersnatch VRF (#14412)

* Introduce bandersnatch vrf

* Some documentation

* Fix tests

* Fix docs refs

* Some more docs

* Comments about key derivation

* Make clippy happy

* Fix ring context enc/dec test

* Fix docs

* Switch to upstream ring-vrf

* Use sub-domains to construct VrfInput

* Bandersnatch VRF experimental feature

* Restore upstream dep

* Fix feature flags

* Apply typo fix

Co-authored-by: Anton <anton.kalyaev@gmail.com>

* Bump bandersnatch-vrfs

* Weiestrass form has been selected

* Rename bandersnatch testing app crypto id

* Support for seed recovery

* Clarified domain size <-> key size relationship

* cargo fmt

* Trigger CI

* Some required tweaks to crypto types

* Remove leftovers from Cargo.toml

* Remove some TODO notes

* Simplification of structs construction

* Trigger CI

* Apply review suggestion

Co-authored-by: Koute <koute@users.noreply.github.com>

* Docs typo

* Fix keystore tests

* Consistence

* Add ref to git rependency

* Static check of MAX_VRF_IOS value

* Clarify behavior for out of ring keys signatures

* Add test for ring-vrf to the keystore

* Fix docs

---------

Co-authored-by: Anton <anton.kalyaev@gmail.com>
Co-authored-by: Koute <koute@users.noreply.github.com>

substrate/primitives/keyring/Cargo.toml

@@ -18,3 +18,9 @@ lazy_static = "1.4.0"
 strum = { version = "0.24.1", features = ["derive"], default-features = false }
 sp-core = { version = "21.0.0", path = "../core" }
 sp-runtime = { version = "24.0.0", path = "../runtime" }
+
+[features]
+# This feature adds Bandersnatch crypto primitives.
+# It should not be used in production since the implementation and interface may still
+# be subject to significant changes.
+bandersnatch-experimental = ["sp-core/bandersnatch-experimental"]