`pac solution add-reference` does not work with Dependent Assembly plugin project

Calling pac solution pack (version: 1.19.4+gfbe2fd6) with mapping file does not map pluginpackages. To reproduce:

1. pack plugin init a new plugin and build it
2. open plugin registration tool pac tool prt and choose "Register New Package" to upload the nupkg created at step 1
3. Ensure the Plugin Package has been added to your solution, export and unpack the solution using pac solution export and pac solution unpack
4. pack the solution using pac solution pack -m mapping.xml -etcetc where the mapping.xml file contains the an entry similar tot he following:

<FileToFile 
	map="prefix_XXXXXXXX.nupkg" 
	to="..\..\PATH_TO_PLUGIN_PROJECT\bin\Release\XXXXXXXX.1.0.0.nupkg" 
/>  

or

<FileToFile 
	map="pluginpackages\prefix_XXXXXXXX\package\prefix_XXXXXXXX.nupkg" 
	to="..\..\PATH_TO_PLUGIN_PROJECT\bin\Release\XXXXXXXX.1.0.0.nupkg" 
/>  

Reproduce the workflow using pack plugin init, pac solution export, pac solution unpack, and pac solution pack -m mapping.xml. Compare the two FileToFile mappings for the plugin package and determine what mapping behavior is expected; done means the dependent assembly plugin package is included correctly when the solution is packed.