Language specific default overrides not marked in settings UI

[isidorn]

Testing #145588

1. Settings UI, open Workspace tab
2. Search for @lang:markdown wordwrap
3. Notice how the wordwrap appears as not changed (no blue line) -> 🐛

wordwrap should be rendered as modified since none of my workspace settings actually change the word wrap value, and the markdown default value should take precedence here.

fyi @sandy081

[rzhao271]

If the default value has been overridden by the markdown language/extension, there should be a badge, or some text. That part is a bug.
I'm not sure about showing a blue line, though, because to me that means the workspace-scope setting value has been manually configured.

[rzhao271]

Tracking in #148672. We already have default override indicators for when an extension contributes a non-language-specific setting default value override, but we currently don't have them for extension-contributed language-specific setting default value overrides.