The (multi-line) string Debug Visualizer previously available for Delphi 2005 to 2007 is now also implemented for Delphi 10.2 using the OTAPI interface. It shows the content of a string without quotes and with line breaks if it contains any.
The implementation was much more complex than I thought. Originally I just used a simple form to implement the interfaces, but that killed the IDE every time a program exited or was reset in the debugger. So now it is based on the StringListVisualizer sample code that comes with Delphi.
These samples are installed in the Source\Visualizers subdirectory of every Delphi installation since Delphi 2010. However, Embarcadero has not provided a dpk file for them, so searching for samplevisualizers.dpk (which is the package filename used by Embarcadero) will not find them.
The source code is on SourceForge.