Fix up particle emitter to work with Atom (#626)

* Fix up particle emitter component to work with Atom

* PR feedback and disable render target tests until supported

Gems/LyShine/Code/Tests/SpriteTest.cpp

@@ -68,6 +68,7 @@ namespace UnitTest
         AZStd::unique_ptr<DataMembers> m_data;
     };
 
+#ifdef LYSHINE_ATOM_TODO // [LYN-3359] - render target support using Atom
     TEST_F(LyShineSpriteTest, Sprite_CanAcquireRenderTarget)
     {
         // initialize to create the static sprite cache
@@ -130,6 +131,7 @@ namespace UnitTest
         CSprite::Shutdown();
         delete mockTexture;
     }
+#endif
 } //namespace UnitTest
 
 AZ_UNIT_TEST_HOOK(DEFAULT_UNIT_TEST_ENV);