Original issues name: Base layer is ignored when profile setting is deleted in SUI

The following bug report is a particular example of inheritance not being represented properly in the Settings UI. In order to fix this, #8269 needs to be implemented.

Environment

Windows build number: 10.0.21286.0
Windows Terminal version (if applicable): 1.6.10101.0

Any other software?

Steps to reproduce

Apply a setting in Base layer, then remove the same setting from a specific profile. For example, set the Base layer font face to Cascadia Code and remove Cascadia Code PL from the font face section of PowerShell.

Note that I didn't test other settings with Base layer, so this may be the only one I'm not entirely sure.

Expected behavior

PowerShell should use Cascadia Code because it's defined in Base layer.

Actual behavior

Terminal shows an error saying "" is not a font face, using Consolas instead. and Cascadia Code is ignored from the Base layer.