Kotlin - Enable trailing comma (#3959)

Trailing commas on Kotlin sources [has many
advantages](https://pinterest.github.io/ktlint/0.49.0/rules/standard/#trailing-comma-on-call-site):
- It makes version-control diffs cleaner – as all the focus is on the
changed value.
- It makes it easy to add and reorder elements – there is no need to add
or delete the comma if you manipulate elements.
- It simplifies code generation, for example, for object initializers.
The last element can also have a comma.

This PR doesn't go as far as require it, but tweaks KtLint to at least
allow it.

The two `.kt` files prove that the KtLint rules have been properly
disabled.

app/src/main/java/com/keylesspalace/tusky/components/report/Screen.kt

@@ -20,5 +20,5 @@ enum class Screen {
     Note,
     Done,
     Back,
-    Finish
+    Finish,
 }

app/src/main/java/com/keylesspalace/tusky/components/scheduled/ScheduledStatusActivity.kt

@@ -163,8 +163,8 @@ class ScheduledStatusActivity :
                 visibility = item.params.visibility,
                 scheduledAt = item.scheduledAt,
                 sensitive = item.params.sensitive,
-                kind = ComposeActivity.ComposeKind.EDIT_SCHEDULED
-            )
+                kind = ComposeActivity.ComposeKind.EDIT_SCHEDULED,
+            ),
         )
         startActivity(intent)
     }