Fix python fbx tests (#2171)

* Update fbx test dbgsg files

Remove rc products from fbx test expected output
Update warning counts for 2 of the tests - these are due to missing material properties
Add SkipAtomOutput setting to disable atom material and mesh processing in scene as these pull in a lot of external dependencies to Process
Removed BlendShapeData and MeshData debug output of positions/normals/faces
Updated ManifestImportRequestHandler to remove warning about Joining 2 absolute paths
Updated AssImpMaterialImporter to use new GenerateRelativeSourcePath API to fix issue where relative path generation failed with tmp project directories

Signed-off-by: amzn-mike <80125227+amzn-mike@users.noreply.github.com>

* Add comment for setting

Signed-off-by: amzn-mike <80125227+amzn-mike@users.noreply.github.com>

* Add override dbgsg file to python test

The mesh optimizer specifically avoids creating optimized nodes for nodes that are not selected, resulting in a different scene graph that requires a different dbgsg file to compare with

Signed-off-by: amzn-mike <80125227+amzn-mike@users.noreply.github.com>

* Replace hardcoded passing of specific registry setting to instead pass all registry settings to AssetBuilder

Signed-off-by: amzn-mike <80125227+amzn-mike@users.noreply.github.com>

Code/Tools/SceneAPI/SceneCore/Import/ManifestImportRequestHandler.cpp

@@ -21,6 +21,7 @@
 
 #include <AzCore/Settings/SettingsRegistryMergeUtils.h>
 #include <AzCore/UserSettings/UserSettingsComponent.h>
+#include <AzCore/Utils/Utils.h>
 
 namespace AZ
 {