TDF and TDF script changes (application changes pending):

- Added new `pad` element to TDFs
- Refactored `pin` and `signal` elements to accommodate new `pad` element
- Improved validation of signal-to-pad relation in TDF validation script
- Added key attribute to `variant` element
- Removed `package` attribute from `variant` element

build/scripts/Targets/TargetDescriptionFiles/Variant.php

@@ -3,14 +3,14 @@ namespace Targets\TargetDescriptionFiles;
 
 class Variant
 {
+    public ?string $key = null;
     public ?string $name = null;
     public ?string $pinoutKey = null;
-    public ?string $package = null;
 
-    public function __construct(?string $name, ?string $pinoutKey, ?string $package)
+    public function __construct(?string $key, ?string $name, ?string $pinoutKey)
     {
+        $this->key = $key;
         $this->name = $name;
         $this->pinoutKey = $pinoutKey;
-        $this->package = $package;
     }
 }