launchd+targets/darwin: Escape XML in plists (#7356)

This patch updates all usage of toPlist such that it escapes any strings
in the final output.

The motication for this change is to avoid confusion when end-users of
home-manager's APIs are not aware that the option values they set end up
being passed un-escaped to XML files.

BREAKING CHANGE: Consumers doing manual escaping will now be doubly escaped.

Co-authored-by: Linnnus <linnnus@users.noreply.github.com>

modules/launchd/default.nix

@@ -43,7 +43,7 @@ let
       };
     };
 
-  toAgent = config: pkgs.writeText "${config.Label}.plist" (toPlist { } config);
+  toAgent = config: pkgs.writeText "${config.Label}.plist" (toPlist { escape = true; } config);
 
   agentPlists = lib.mapAttrs' (n: v: lib.nameValuePair "${v.config.Label}.plist" (toAgent v.config)) (
     lib.filterAttrs (n: v: v.enable) cfg.agents

modules/launchd/launchd.nix

@@ -155,6 +155,18 @@ in
         This key maps to the second argument of `execvp(3)`.  This key is required in the absence of the Program
         key. Please note: many people are confused by this key. Please read `execvp(3)` very carefully!
       '';
+      # TODO: Remove this some time after 25.01.
+      apply =
+        value:
+        if value != null then
+          map (
+            item:
+            lib.warnIf (lib.hasInfix "&" item)
+              "A value for `ProgramArguments` contains the literal string `&`. This is no longer necessary and will lead to double-escaping, as home-manager now automatically escapes special characters."
+              item
+          ) value
+        else
+          value;
     };
 
     EnableGlobbing = mkOption {