Add "Control flow with empty body" inspection

#KT-30970 Fixed

idea/testData/inspectionsLocal/controlFlowWithEmptyBody/when/block.kt

@@ -0,0 +1,7 @@
+// PROBLEM: 'when' has empty body
+// FIX: none
+
+fun test(i: Int) {
+    <caret>when (i) {
+    }
+}

idea/testData/inspectionsLocal/controlFlowWithEmptyBody/when/block2.kt

@@ -0,0 +1,7 @@
+// PROBLEM: 'when' has empty body
+// FIX: none
+
+fun test() {
+    <caret>when (val i = 1) {
+    }
+}

idea/testData/inspectionsLocal/controlFlowWithEmptyBody/when/blockHasComment.kt

@@ -0,0 +1,8 @@
+// PROBLEM: 'when' has empty body
+// FIX: none
+
+fun test(i: Int) {
+    <caret>when (i) {
+        // comment
+    }
+}

idea/testData/inspectionsLocal/controlFlowWithEmptyBody/when/blockHasStatement.kt

@@ -0,0 +1,7 @@
+// PROBLEM: none
+
+fun test(i: Int) {
+    <caret>when (i) {
+        else -> {}
+    }
+}