re-import support (from both actions and toolkit)

[Danielmelody]

To get it work on 4.20 and later, #4 should be merged too.

[Danielmelody]

This is necessary when working with external text editors, to simplify workflow and reduce inconsistency

[samrrr]

When you use this asset commit, you should put
pTextAsset->Modify();
To TextAssetFactory.cpp 107 line:
if (FFileHelper::LoadFileToString(NewText, *ResolvedSourceFilePath))
{
pTextAsset->Text = NewText;
pTextAsset->Modify();
return EReimportResult::Succeeded;
}

[Danielmelody]

@samrrr Thanks, added it.