Qute - support multiple NamespaceResolvers for the same namespace

[mkouba]

Currently, only one NamespaceResolver can be registered for a specific namespace (such as inject or data). The original idea was to keep the implementation simple. However, a NamespaceResolver could implement io.quarkus.qute.WithPriority as the regular value resolvers do so that the resolver with higher priority would take precedence. This would be especially helpful when adding built-in template extensions that can potentially conflict with user-defined extensions.

• NamespaceResolver implements WithPriority
• EngineBuilder.addNamespaceResolver() should not throw IllegalArgumentException anymore
• EvaluatorImpl.evaluate() should iterate over all matching namespace resolvers
• Template extension methods that share the same namespace needn't be declared on the same class anymore
• ExtensionMethodGenerator should group the template extension methods that share the same namespace and priority