misleading root folder size in footprint reports

[ktaborowski]

Is your enhancement proposal related to a problem? Please describe.
The problem is in ram (and rom) report generated with ninja ram_report command.
It is described based on the ascii tree view, but it impacts .json report also.

The size of root folder in report is misleading, as it describes only the symbols without parent folder, but not the folders (incoherent behavior).

Path                 Size    %   
=================================
root                   40 11.76% 
├── sym1               10 2.94%  
├── sym2               10 2.94%  
├── folder1           100 29.41% 
│   └── source1.c     100 29.41% 
│       ├── item11     50 0.40%  
│       └── item12     50 2.16%  
├── sym3               10 2.94%  
├── folder2           200 58.82% 
│   └── source2.c     200 58.82% 
│       ├── item21    100 29.41% 
│       └── item22    100 29.41% 
└── sym4               10 2.94%  
=================================
                      340        

Describe the solution you'd like
I would like the report to group all "free" symbols in the generic folder (the exemplary name _unassigned used in snippet below).
The root size would be the size of all elements.

Path                 Size    %   
=================================
root                  340 100.00%   
├── folder1           100 29.41% 
│   └── source1.c     100 29.41% 
│       ├── item11     50 0.40%  
│       └── item12     50 2.16%   
├── folder2           200 58.82% 
│   └── source2.c     200 58.82% 
│       ├── item21    100 29.41% 
│       └── item22    100 29.41% 
└── _unassigned        40 11.76% 
    ├── sym1           10 2.94% 
    ├── sym2           10 2.94% 
    ├── sym3           10 2.94% 
    └── sym4           10 2.94%  
=================================
                      340