Format spaces around by keyword (#1016)

idea/testData/formatter/By.after.kt

@@ -0,0 +1,4 @@
+class Bar(val r: Runnable) : Runnable by r
+class Foo {
+    val bar by lazy { "" }
+}

idea/testData/formatter/By.kt

@@ -0,0 +1,4 @@
+class Bar(val r: Runnable) : Runnable    by  r
+class Foo {
+    val bar   by    lazy { "" }
+}