JwtDecoders and NimbusJwtDecoder should use the same JWKSource

[jzheaux]

Related to #9991

JwtDecoders and ReactiveJwtDecoders instantiate a RemoteJWKSet in order to discover reasonable defaults for the JWS algorithms a resource server should accept. NimbusJwtDecoder and NimbusReactiveJwtDecoder both instantiate a JWK source as well in order to collect the keys needed to verify JWT signatures.

It would be nice if these shared the same instance. If so, then once JwtDecoders makes a query for the JWK Set, it's already cached for future decode requests.

This is especially nice with the introduction of SupplierJwtDecoder, which lazily loads the NimbusJwtDecoder. Without this proposed optimization, using SupplierJwtDecoder and JwtDecoders together would mean that the first decode request would experience three HTTP calls instead of two.