Add JSON debug data interface

src/App.svelte

 <script lang="ts">
+    import { element } from "svelte/internal";
 import type { WorkPackage } from "./estimator";
     import RowWorkItem from "./RowWorkItem.svelte";
     import SumRow from "./SumRow.svelte";
@@ -10,6 +11,7 @@
         workPackages.push({a: null, b:null, c: null});
     }
     $: dataJson = JSON.stringify(workPackages, null, 2)
+    let jsonPasteArea = "";
 </script>
 
 <main>
@@ -30,6 +32,38 @@
             <SumRow {workPackages}></SumRow>
         </tbody>
     </table>
+    <details>
+        <summary>
+            Debug: Show Input as JSON
+        </summary>
+        <pre>
+            {dataJson}
+        </pre>
+    </details><details>
+        <summary>
+            Debug: Paste Input as JSON
+        </summary>
+        <textarea bind:value="{jsonPasteArea}" on:input={() => {
+            if (jsonPasteArea.trim().length === 0) return
+            try {
+                const decoded = JSON.parse(jsonPasteArea.trim());
+                if (!Array.isArray(decoded))
+                    throw TypeError("Input must be an array")
+                for (const elem of decoded) {
+                    if (typeof elem.a !== 'number' && elem.a !== null)
+                        throw TypeError("An 'a' attribute was neither number not null");
+                    if (typeof elem.b !== 'number' && elem.b !== null)
+                        throw TypeError("An 'b' attribute was neither number not null");
+                    if (typeof elem.c !== 'number' && elem.c !== null)
+                        throw TypeError("An 'c' attribute was neither number not null");
+                }
+                workPackages = decoded;
+                jsonPasteArea = "";
+            } catch (error) {
+                alert(error.toString())
+            }
+        }}/>
+    </details>
 </main>
 
 <a href="https://gitlab.fachschaften.org/jfowl/swk-project-effort-estimation"