Enhance Start-SPMigration GUI for SharePoint SSOM compatibility and update mapping schema

- Added version checks to ensure the script runs in 64-bit Windows PowerShell Desktop Edition.
- Implemented checks for STA thread requirement and SharePoint environment validation.
- Updated application version to 1.2.0 and supported mapping schema version to 2.
- Introduced a new function to retrieve SharePoint product support information based on build version.
- Modified mapping table structure to include ToolVersion and additional metadata fields.
- Updated sample mapping JSON to reflect new schema version and added new fields for metadata column mappings.

mapping.sample.json

@@ -1,7 +1,10 @@
 {
-  "SchemaVersion": 1,
+  "SchemaVersion": 2,
+  "ToolVersion": "1.2.0",
   "GeneratedAtUtc": "2026-04-15T08:00:00.0000000Z",
   "SourceWebUrl": "http://sharepoint/sites/Quelle",
+  "SourceSharePointProduct": "SharePoint Server 2016",
+  "SourceSharePointBuild": "16.0.5508.1000",
   "LibraryMappings": [
     {
       "ObjectType": "DocumentLibrary",
@@ -24,17 +27,24 @@
       "Hidden": false
     }
   ],
-  "MetadataColumnMappings": [
-    {
-      "ObjectType": "DocumentLibrary",
-      "ContainerSourceTitle": "Documents",
-      "SourceInternalName": "DHS2016Persdat",
-      "TargetInternalName": "Persdat",
-      "DisplayName": "Personaldaten",
-      "TypeAsString": "Text",
-      "Hidden": false,
-      "ReadOnly": false,
-      "Sealed": false
-    }
-  ]
-}
+  "MetadataColumnMappings": {
+    "SystemColumns": [],
+    "CustomColumns": [
+      {
+        "ObjectType": "DocumentLibrary",
+        "ContainerSourceTitle": "Documents",
+        "SourceInternalName": "DHS2016Persdat",
+        "SourceCanonicalInternalName": "DHS2016Persdat",
+        "SourceSupportingInternalNames": [],
+        "TargetInternalName": "Persdat",
+        "DisplayName": "Personaldaten",
+        "TypeAsString": "Text",
+        "Hidden": false,
+        "ReadOnly": false,
+        "Sealed": false,
+        "IsSystemColumn": false,
+        "ImportSupported": true
+      }
+    ]
+  }
+}