fix(dart_indent): Fix dart case/default indent

add tests

add tests for fallthrough case

add more tests

keep functional tests

tests/indent/dart/switch.dart

@@ -0,0 +1,30 @@
+void test() {
+  switch(a) {
+    case 1:
+  }
+}
+
+void test() {
+  switch(a) {
+    default:
+  }
+}
+
+void test_break_dedent() {
+  switch(x) {
+    case 1:
+      break;
+  }
+  switch(y) {
+    case 2:
+      return;
+  }
+}
+
+
+void test_multi_case() {
+  switch(x) { 
+    case 1:
+    case 2:
+  }
+}