Add DependenciesProvider

Sources/ElixxirDAppsSDK/DependenciesProvider.swift

+import Bindings
+
+public struct DependenciesProvider {
+  public var get: () -> String
+
+  public func callAsFunction() -> String {
+    get()
+  }
+}
+
+extension DependenciesProvider {
+  public static let live = DependenciesProvider(get: BindingsGetDependencies)
+}
+
+#if DEBUG
+extension DependenciesProvider {
+  public static let failing = DependenciesProvider { fatalError("Not implemented") }
+}
+#endif