The Build Action of the tsconfig.json file has to be set to Content.
Otherwise Visual Studio ignores this file since VS 2019.
There is a downside though: After this change VS 2017 will complain about the Build Action:
Error NETSDK1022
Duplicate 'Content' items were included. The .NET SDK includes 'Content' items from your project directory by default. You can either remove these items from your project file, or set the 'EnableDefaultContentItems' property to 'false' if you want to explicitly include them in your project file. For more information, see https://aka.ms/sdkimplicititems. The duplicate items were: 'tsconfig.json'
