Add formatting rule "new line between { and when entry"

idea/testData/formatter/WhenBraceAndEntry.after.kt

@@ -0,0 +1,5 @@
+fun foo(x: Int) = when (x) {
+    1 -> 2
+    3 -> 4
+    else -> 6
+}

idea/testData/formatter/WhenBraceAndEntry.kt

@@ -0,0 +1,4 @@
+fun foo(x: Int) = when(x) { 1 -> 2
+    3 -> 4
+    else -> 6
+}