feat(iOS): add open func instanceCapacitorBridge

[tossaro]

When I want to register plugins manually, registerPluginType on CapacitorBridge is blocked by autoRegisterPlugins that by default set to true.
So, we need some open function that return CapacitorBridge instance on CAPBridgeViewController:
open func instanceCapacitorBridge(_ configDescriptor: InstanceDescriptor, _ configuration: InstanceConfiguration, _ assetHandler: WebViewAssetHandler, _ delegationHandler: WebViewDelegationHandler) -> CapacitorBridge { return CapacitorBridge(with: configuration, delegate: self, cordovaConfiguration: configDescriptor.cordovaConfiguration, assetHandler: assetHandler, delegationHandler: delegationHandler) }