Move startstop1 uid finding feature into a separate component

This is a general cleanup to make it clear how to reuse this
functionality from elsewhere if that is needed.

CMakeLists.txt

@@ -207,6 +207,7 @@ set (VENUS_QML_MODULE_SOURCES
     components/GaugeModel.qml
     components/GaugeHeader.qml
     components/GeneratorManualControlButton.qml
+    components/GensetStartStop1Finder.qml
     components/EvChargerStatusModel.qml
     components/FlatListItemSeparator.qml
     components/GeneratorIconLabel.qml

components/GensetStartStop1Finder.qml

@@ -0,0 +1,62 @@
+/*
+** Copyright (C) 2024 Victron Energy B.V.
+** See LICENSE.txt for license information.
+*/
+
+import QtQuick
+import Victron.VenusOS
+
+/*
+	This component provides a way to find the startstop1 uid for a genset service.
+	On D-Bus this is always "com.victronenergy.generator.startstop1", but on a MQTT backend this
+	is less easily located.
+
+	For some background context, there are two start/stop generator types:
+
+	- startstop0
+		The original start/stop generator. This turns the Cerbo's built-in relay on/off.
+		On D-Bus, the uid is "com.victronenergy.generator.startstop0".
+		On MQTT, the service uid is "mqtt/generator/0".
+
+	- startstop1
+		This works with an actual genset, by sending a command to it instead of closing the relay.
+		That is, it controls any genset service with start-stop capabilities that can be remotely
+		commanded. For example, FischerPanda, CompAp and DSE controllers.
+
+		On D-Bus, the uid is "com.victronenergy.generator.startstop1".
+		On MQTT, the service uid is found by locating the generator service with a /GensetService
+			value that matches that of a genset or dcgenset service. It might turn out to be
+			"mqtt/generator/1", but that is not guaranteed.
+
+	So, unlike for many other service types, these services these do not refer to different generator
+	instances; instead, they are used to distinguish between two different types of generators.
+*/
+
+QtObject {
+	id: root
+
+	property string gensetServiceUid
+
+	// On D-Bus, the startstop1 generator is at com.victronenergy.generator.startstop1.
+	// On MQTT, the startstop1 generator is the one with GensetService=com.victronenergy.genset.*
+	// (or GensetService=com.victronenergy.dcgenset.* if this is a dcgenset)
+	readonly property string startStop1Uid: BackendConnection.type === BackendConnection.MqttSource
+			? _generatorWithGensetService
+			: BackendConnection.uidPrefix() + "/com.victronenergy.generator.startstop1"
+
+	property string _generatorWithGensetService
+
+	readonly property Instantiator _generatorObjects: Instantiator {
+		model: BackendConnection.type === BackendConnection.MqttSource ? Global.generators.model : null
+		delegate: VeQuickItem {
+			uid: model.device.serviceUid + "/GensetService"
+			onValueChanged: {
+				const serviceType = BackendConnection.serviceTypeFromUid(root.gensetServiceUid)
+				if ( (isValid && serviceType === "dcgenset" && value.startsWith("com.victronenergy.dcgenset."))
+						|| (isValid && serviceType !== "dcgenset" && value.startsWith("com.victronenergy.genset.")) ) {
+						root._generatorWithGensetService = model.device.serviceUid
+				}
+			}
+		}
+	}
+}

components/PageGensetModel.qml

@@ -11,30 +11,8 @@ ObjectModel {
 
 	property string bindPrefix
 	property string settingsBindPrefix: Global.systemSettings.serviceUid + "/Settings/Generator1"
-	property string startStopBindPrefix: startStop1Uid
+	property string startStopBindPrefix: _startStop1Finder.startStop1Uid
 	readonly property string serviceType: BackendConnection.serviceTypeFromUid(bindPrefix)
-
-	// On D-Bus, the startstop1 generator is at com.victronenergy.generator.startstop1.
-	// On MQTT, the startstop1 generator is the one with GensetService=com.victronenergy.genset.*
-	// (or GensetService=com.victronenergy.dcgenset.* if this is a dcgenset)
-	readonly property string startStop1Uid: BackendConnection.type === BackendConnection.MqttSource
-			? generatorWithGensetService
-			: BackendConnection.uidPrefix() + "/com.victronenergy.generator.startstop1"
-	property string generatorWithGensetService
-
-	property Instantiator generatorObjects: Instantiator {
-		model: BackendConnection.type === BackendConnection.MqttSource ? Global.generators.model : null
-		delegate: VeQuickItem {
-			uid: model.device.serviceUid + "/GensetService"
-			onValueChanged: {
-				if ( (isValid && root.dcGenset && value.startsWith("com.victronenergy.dcgenset."))
-						|| (isValid && !root.dcGenset && value.startsWith("com.victronenergy.genset.")) ) {
-						root.generatorWithGensetService = model.device.serviceUid
-				}
-			}
-		}
-	}
-
 	readonly property bool dcGenset: serviceType === "dcgenset"
 	readonly property int nrOfPhases: phases.isValid ? phases.value
 												   : dcGenset ? 0
@@ -47,6 +25,10 @@ ObjectModel {
 		uid: root.startStopBindPrefix ? root.startStopBindPrefix + "/Enabled" : ""
 	}
 
+	readonly property GensetStartStop1Finder _startStop1Finder: GensetStartStop1Finder {
+		gensetServiceUid: root.bindPrefix
+	}
+
 	PrimaryListLabel {
 		allowed: root.gensetEnabled.value === 0
 		//% "This genset controller requires a helper relay to be controlled but the helper relay is not configured. Please configure Relay 1 under Settings → Relay to \"Connected genset helper relay\"."