IDE: Fix formatting of closing square brackets

Previously closing square brackets would be caught in the logic for
elements in collections, indenting them to the same level. Now they are
indented with the normal non-sibling logic, which indents them
correctly.

test/SourceKit/CodeFormat/indent-closing-array.swift

@@ -0,0 +1,26 @@
+struct Foo {
+    let bar = [
+        1,
+        2,
+    ]
+
+    func baz() {
+        let qux = [
+            "a": 1,
+            "b": 2,
+        ]
+
+        let quxx = [
+            "a": 1,
+            "b": 2
+        ]
+    }
+}
+
+// RUN: %sourcekitd-test -req=format -line=5 -length=1 %s >%t.response
+// RUN: %sourcekitd-test -req=format -line=11 -length=1 %s >>%t.response
+// RUN: %sourcekitd-test -req=format -line=16 -length=1 %s >>%t.response
+// RUN: %FileCheck --strict-whitespace %s <%t.response
+// CHECK: key.sourcetext: "    ]"
+// CHECK: key.sourcetext: "        ]"
+// CHECK: key.sourcetext: "        ]"