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/TargetDescriptionFile.php

@@ -17,6 +17,7 @@ require_once __DIR__ . "/Module.php";
 require_once __DIR__ . "/RegisterGroup.php";
 require_once __DIR__ . "/RegisterGroupReference.php";
 require_once __DIR__ . "/Register.php";
+require_once __DIR__ . "/Pad.php";
 require_once __DIR__ . "/Pinout.php";
 require_once __DIR__ . "/Variant.php";
 require_once __DIR__ . "/TargetFamily.php";
@@ -47,6 +48,9 @@ class TargetDescriptionFile
     /** @var Module[] */
     public array $modules = [];
 
+    /** @var Pad[] */
+    public array $pads = [];
+
     /** @var Pinout[] */
     public array $pinouts = [];
 
@@ -236,6 +240,17 @@ class TargetDescriptionFile
         $module->key = $newKey;
     }
 
+    public function getPad(string $key): ?Pad
+    {
+        foreach ($this->pads as $pad) {
+            if ($pad->key === $key) {
+                return $pad;
+            }
+        }
+
+        return null;
+    }
+
     public function getPinout(string $key): ?Pinout
     {
         foreach ($this->pinouts as $pinout) {