Assimp FBX Import support

Issues fixed:
- Updated assimp to latest and backported fixes into godot.
- Fixed file scale being ignored from FBX file.
- Fixed bone removal
- Implemented proper armature binding
- Fixed recursion not always going through the entire path
- Implemented assimp global scaling system
- Fixed assimp global scale process to support unit conversion
- Implemented proper fbx scaling
- Fixed asserts caused by missing faces in some models which could crash
- Fixed valid bone removal
- Fixed root node being overwriten by assimp which caused data loss
- Fixed armature construction so that it works with multiple roots
- Implemented basic support for FBX standard materials
- Refactoring to improve code quality and improve function reuse.
- Simplified node creation from assimp scene into subsections: create_light, create_mesh, create_bone.
- Creating meshes is now done after hierarchy is created so that the skeleton is always available.
- Added support to assimp to support file scale in all formats which call SetFileScale.
- Many other fixes provided into assimp.

Known issues:
- FBX pivots from Maya do not currently work. (workaround: for now use blender import and export to remove pivot tracks)
- Hierarchy creates an extra node for each mesh - this was done intentionally but we intended to do a pass to remove these as they're a required node.
- When an animated mesh has not executed any animation the rest pose is wrong.

Co-authored-by: K. S. Ernest (iFire) Lee <ernest.lee@chibifire.com>

thirdparty/assimp/code/Common/BaseImporter.cpp

@@ -76,9 +76,25 @@ BaseImporter::~BaseImporter() {
     // nothing to do here
 }
 
+void BaseImporter::UpdateImporterScale( Importer* pImp )
+{
+    ai_assert(pImp != nullptr);
+    ai_assert(importerScale != 0.0);
+    ai_assert(fileScale != 0.0);
+
+    double activeScale = importerScale * fileScale;
+
+    // Set active scaling
+    pImp->SetPropertyFloat( AI_CONFIG_APP_SCALE_KEY, activeScale);
+
+    ASSIMP_LOG_DEBUG_F("UpdateImporterScale scale set: %f", activeScale );
+}
+
 // ------------------------------------------------------------------------------------------------
 // Imports the given file and returns the imported data.
-aiScene* BaseImporter::ReadFile(const Importer* pImp, const std::string& pFile, IOSystem* pIOHandler) {
+aiScene* BaseImporter::ReadFile(Importer* pImp, const std::string& pFile, IOSystem* pIOHandler) {
+
+
     m_progress = pImp->GetProgressHandler();
     if (nullptr == m_progress) {
         return nullptr;
@@ -100,6 +116,11 @@ aiScene* BaseImporter::ReadFile(const Importer* pImp, const std::string& pFile,
     {
         InternReadFile( pFile, sc.get(), &filter);
 
+        // Calculate import scale hook - required because pImp not available anywhere else
+        // passes scale into ScaleProcess
+        UpdateImporterScale(pImp);
+
+
     } catch( const std::exception& err )    {
         // extract error description
         m_ErrorText = err.what();
@@ -112,7 +133,7 @@ aiScene* BaseImporter::ReadFile(const Importer* pImp, const std::string& pFile,
 }
 
 // ------------------------------------------------------------------------------------------------
-void BaseImporter::SetupProperties(const Importer* /*pImp*/)
+void BaseImporter::SetupProperties(const Importer* pImp)
 {
     // the default implementation does nothing
 }
@@ -588,6 +609,8 @@ aiScene* BatchLoader::GetImport( unsigned int which )
     return nullptr;
 }
 
+
+
 // ------------------------------------------------------------------------------------------------
 void BatchLoader::LoadAll()
 {