cosmic: Provide CosmicConfigEntry impl, use _ in property names

It seems to derive `CosmicConfigEntry`, we need to use `_` in property
names, because `_` isn't mapped to `-` and there doesn't seem to be a
mechanism like `#[serde(rename)]`.

It seems good to be consistent anyway. So this seems good to change,
unless we really like using `-` for names on disk, then cosmic-panel
needs to be changed.

`CosmicConfigEntry` also requires `PartialEq`, which is easy enough to
add.

This will break existing input settings, which will have to be
re-applied with the new locations. Cosmic-settings also need to be
updated for this.

cosmic-comp-config/src/workspace.rs

@@ -6,7 +6,7 @@ fn default_workspace_layout() -> WorkspaceLayout {
     WorkspaceLayout::Vertical
 }
 
-#[derive(Debug, Clone, Serialize, Deserialize)]
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 pub struct WorkspaceConfig {
     pub workspace_mode: WorkspaceMode,
     pub workspace_amount: WorkspaceAmount,