ATOM-16747 RPISystemInterface::GetDefaultScene returns the scene crea… (#5153) (#5389)

* ATOM-16747 RPISystemInterface::GetDefaultScene returns the scene created by PreviewRenderer but not the Main Scene
Deprecate GetDefaultScene() function.
Update all the places which use GetDefaultScene to use Scene::GetFeatureProcessorFromEntityId or GetMainScene.
Tested with Editor, UI Editor, Material Editor, game launcher.

Signed-off-by: Qing Tao <55564570+VickyAtAZ@users.noreply.github.com>
(cherry picked from commit 8da6bea073)

Gems/AtomLyIntegration/AtomFont/Code/Include/AtomLyIntegration/AtomFont/FFont.h

@@ -133,18 +133,6 @@ namespace AZ
         typedef std::vector<FontEffect> FontEffects;
         typedef FontEffects::iterator FontEffectsIterator;
 
-        struct FontPipelineStateMapKey
-        {
-            AZ::RPI::SceneId m_sceneId;         // which scene pipeline state is attached to (via Render Pipeline)
-            AZ::RHI::DrawListTag m_drawListTag; // which render pass this pipeline draws in by default
-
-            bool operator<(const FontPipelineStateMapKey& other) const
-            {
-                return m_sceneId < other.m_sceneId
-                       ||      (m_sceneId == other.m_sceneId && m_drawListTag < other.m_drawListTag);
-            }
-        };
-
         struct FontShaderData
         {
             AZ::RHI::ShaderInputNameIndex m_imageInputIndex = "m_texture";