ATOM-16237 Using setting registry to RPI system settings (#3663)

* ATOM-16237 Using setting registry to RPI system settings
Changes include:
- Remove RHISystemDesriptor since the pre-registered draw list tag is not needed.
- Remove EitorContext which was for system component settings.
- Add atom_rpi.setreg file
- Add getting RPISystemDescriptor from setting registry.

Signed-off-by: qingtao <qingtao@amazon.com>

Gems/LyShine/Code/Source/LyShineSystemComponent.cpp

@@ -205,6 +205,10 @@ namespace LyShine
     ////////////////////////////////////////////////////////////////////////////////////////////////////
     void LyShineSystemComponent::Deactivate()
     {
+#if !defined(LYSHINE_BUILDER) && !defined(LYSHINE_TESTS)
+        m_loadTemplatesHandler.Disconnect();
+#endif
+
         UiSystemBus::Handler::BusDisconnect();
         UiSystemToolsBus::Handler::BusDisconnect();
         UiFrameworkBus::Handler::BusDisconnect();