feat(niri/workspaces): add window icons via window-rewrite

Adds format-window-separator, window-rewrite and window-rewrite-default
options plus the {windows} format replacement to the niri/workspaces
module (rebased onto master; coexists with ignore-workspaces).

man/waybar-niri-workspaces.5.scd

@@ -97,6 +97,21 @@ If none of the sorting options are enabled, workspaces keep their output/index o
 	default: [] ++
 	Regexes to match against workspaces names and index's. If there's a match, the workspace will not be shown.
 
+*format-window-separator*: ++
+	typeof: string ++
+	default: " " ++
+	Separator used between window representations generated by *window-rewrite*.
+
+*window-rewrite*: ++
+	typeof: object ++
+	default: {} ++
+	Rules to map window app_id and/or title to a specific string representation (e.g., an icon). Keys are regular expressions matching `app_id<regex>` and/or `title<regex>`. Values are the replacement strings, which can contain `{app_id}` and `{title}` placeholders.
+
+*window-rewrite-default*: ++
+	typeof: string ++
+	default: "?" ++
+	The default representation for windows that don't match any rule in *window-rewrite*.
+
 # FORMAT REPLACEMENTS
 
 *{value}*: Name of the workspace, or index for unnamed workspaces,
@@ -112,6 +127,8 @@ as defined by niri.
 
 *{total}*: The total number of workspaces.
 
+*{windows}*: Concatenated representation of windows in the workspace, using *window-rewrite* rules and *format-window-separator*.
+
 # ICONS
 
 Additional to workspace name matching, the following *format-icons* can be set.
@@ -126,18 +143,26 @@ Additional to workspace name matching, the following *format-icons* can be set.
 
 ```
 "niri/workspaces": {
-	"format": "{icon}",
-	"format-icons": {
-		// Named workspaces
-		// (you need to configure them in niri)
-		"browser": "",
-		"discord": "",
-		"chat": "<b></b>",
+    "format": "{icon} {windows}",
+    "format-window-separator": "|",
+    "window-rewrite-default": "",
+    "window-rewrite": {
+        "app_id<firefox>": "",
+        "app_id<foot>": "",
+        "app_id<org.gnome.Nautilus> title<.*Downloads.*>": "",
+        "app_id<org.gnome.Nautilus>": ""
+    },
+    "format-icons": {
+        // Named workspaces
+        // (you need to configure them in niri)
+        "browser": "",
+        "discord": "",
+        "chat": "<b></b>",
 
-		// Icons by state
-		"active": "",
-		"default": ""
-	}
+        // Icons by state
+        "active": "",
+        "default": ""
+    }
 }
 ```