Small workaround and fix to ensure line fade (alpha) displays correctly (#6733)

Signed-off-by: Tom Hulton-Harrop <82228511+hultonha@users.noreply.github.com>

Code/Framework/AzToolsFramework/AzToolsFramework/Manipulators/ManipulatorSnapping.cpp

@@ -184,6 +184,10 @@ namespace AzToolsFramework
         const float halfGridSquareCount = float(gridSquareCount) * 0.5f;
         const float halfGridSize = halfGridSquareCount * squareSize;
         const float fadeLineLength = cl_viewportFadeLineDistanceScale * squareSize;
+
+        // ensure AuxGeomDraw::OpacityType::Translucent render state is set
+        debugDisplay.SetAlpha(0.5f);
+
         for (size_t lineIndex = 0; lineIndex <= gridSquareCount; ++lineIndex)
         {
             const float lineOffset = -halfGridSize + (lineIndex * squareSize);

Gems/AtomLyIntegration/AtomBridge/Code/Source/AtomDebugDisplayViewportInterface.cpp

@@ -348,14 +348,7 @@ namespace AZ::AtomBridge
     void AtomDebugDisplayViewportInterface::SetAlpha(float a)
     {
         m_rendState.m_color.SetA(a);
-        if (a < 1.0f)
-        {
-            m_rendState.m_opacityType = AZ::RPI::AuxGeomDraw::OpacityType::Opaque;
-        }
-        else
-        {
-            m_rendState.m_opacityType = AZ::RPI::AuxGeomDraw::OpacityType::Translucent;
-        }
+        m_rendState.m_opacityType = a < 1.0f ? AZ::RPI::AuxGeomDraw::OpacityType::Translucent : AZ::RPI::AuxGeomDraw::OpacityType::Opaque;
     }
 
     void AtomDebugDisplayViewportInterface::DrawQuad(