Explicitly require C++20 to build

Otherwise the build fails on Windows due to use of designated
initializers in solarinputmodel.cpp.

Also fix -Wdeprecated-this-capture warnings in backendconnection.cpp
and basedevicemodel.cpp.

CMakeLists.txt

@@ -55,7 +55,7 @@ set(CMAKE_INCLUDE_CURRENT_DIR ON)
 set(CMAKE_AUTOUIC ON)
 set(CMAKE_AUTOMOC ON)
 
-set(CMAKE_CXX_STANDARD 14)
+set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 message("Building VenusOS for ${CMAKE_SYSTEM_NAME}")
 message("CMAKE_CXX_FLAGS: ${CMAKE_CXX_FLAGS}")

src/backendconnection.cpp

@@ -261,7 +261,7 @@ void BackendConnection::initMqttConnection(const QString &address)
 			producer->continueConnect();
 		}
 	});
-	connect(mqttProducer, &VeQItemMqttProducer::connectionStateChanged, this, [=] {
+	connect(mqttProducer, &VeQItemMqttProducer::connectionStateChanged, this, [&mqttProducer, this] {
 		setState(mqttProducer->connectionState());
 	});
 	connect(mqttProducer, &VeQItemMqttProducer::errorChanged,

src/basedevicemodel.cpp

@@ -35,7 +35,7 @@ void BaseDevice::setServiceUid(const QString &serviceUid)
 	}
 
 	if (m_serviceUid != serviceUid) {
-		maybeEmitValidChanged([=]() {
+		maybeEmitValidChanged([serviceUid, this]() {
 			m_serviceUid = serviceUid;
 			emit serviceUidChanged();
 		});
@@ -50,7 +50,7 @@ int BaseDevice::deviceInstance() const
 void BaseDevice::setDeviceInstance(int deviceInstance)
 {
 	if (m_deviceInstance != deviceInstance) {
-		maybeEmitValidChanged([=]() {
+		maybeEmitValidChanged([deviceInstance, this]() {
 			m_deviceInstance = deviceInstance;
 			emit deviceInstanceChanged();
 		});
@@ -78,7 +78,7 @@ QString BaseDevice::productName() const
 void BaseDevice::setProductName(const QString &productName)
 {
 	if (m_productName != productName) {
-		maybeEmitValidChanged([=]() {
+		maybeEmitValidChanged([productName, this]() {
 			m_productName = productName;
 			emit productNameChanged();
 		});
@@ -93,7 +93,7 @@ QString BaseDevice::customName() const
 void BaseDevice::setCustomName(const QString &customName)
 {
 	if (m_customName != customName) {
-		maybeEmitValidChanged([=]() {
+		maybeEmitValidChanged([customName, this]() {
 			m_customName = customName;
 			emit customNameChanged();
 		});