Refactor ISO data type validation from cell to shared date; add extra checks for invalid dates; and appropriate unit tests

tests/data/Cell/SetValueExplicit.php

@@ -1,5 +1,6 @@
 <?php
 
+use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
 
 return [
@@ -39,12 +40,27 @@ return [
         DataType::TYPE_NUMERIC,
     ],
     [
-        '#DIV/0!',
+        44613.43090277778,
+        '2022-02-21 10:20:30',
+        DataType::TYPE_ISO_DATE,
+    ],
+    [
+        44613.0,
+        '2022-02-21',
+        DataType::TYPE_ISO_DATE,
+    ],
+    [
+        -30879.0,
+        '1815-06-15',               // Dates outside the Excel Range should fail really
+        DataType::TYPE_ISO_DATE,
+    ],
+    [
+        ExcelError::DIV0(),
         '#DIV/0!',
         DataType::TYPE_ERROR,
     ],
     [
-        '#NULL!',
+        ExcelError::null(),
         'NOT A VALID ERROR TYPE VALUE',
         DataType::TYPE_ERROR,
     ],