Working on making Material Editor able to open materials that have missing textures.

Made it a warning instead of an error when MaterialAssetCreator can't find a texture.
Updated the Material Editor's MaterialDocument class to not elevate warnings to errors.
Material Editor uses new features in TraceRecorder to show a message dialog when warnings are detected so the user is notified of the missing texture.

Next I will work on making MaterialAssetCreator put a "missing" texture in place of the requested one.

Signed-off-by: santorac <55155825+santorac@users.noreply.github.com>

Gems/Atom/RPI/Code/Source/RPI.Edit/Material/MaterialSourceData.cpp

@@ -329,7 +329,7 @@ namespace AZ
                                     }
                                     else
                                     {
-                                        materialAssetCreator.ReportError(
+                                        materialAssetCreator.ReportWarning(
                                             "Material property '%s': Could not find the image '%s'", propertyId.GetFullName().GetCStr(),
                                             property.second.m_value.GetValue<AZStd::string>().data());
                                     }