feat: expose JUnit Jupiter 6 as a separate Enable Tests option (#1871)

Add a "JUnit Jupiter 6" entry to the framework picker and rename the
existing entry to "JUnit Jupiter 5". `TestKind.JUnit6` already exists
in the API and `getJarIds` already routes JUnit5 to the 1.x line and
JUnit6 to the 6.x line (PR #1868) — this PR is just the UI side of
that split so users can actually pick JUnit 6 from the QuickPick.

Author: wenytang-ms

src/commands/testDependenciesCommands.ts

@@ -98,7 +98,11 @@ async function setupUnmanagedFolder(projectUri: Uri, testKind?: TestKind): Promi
 
 async function getTestKind(): Promise<TestKind | undefined> {
     const framework: any = await window.showQuickPick([{
-        label: 'JUnit Jupiter',
+        label: 'JUnit Jupiter 6',
+        description: 'Recommended',
+        value: TestKind.JUnit6,
+    }, {
+        label: 'JUnit Jupiter 5',
         value: TestKind.JUnit5,
     }, {
         label: 'JUnit',