[FIR2IR] Don't replace while loop and when branch body blocks with single expression. Skip some empty blocks.

https://youtrack.jetbrains.com/issue/KT-60264/K2-while-loop-body-block-sometimes-replaced-with-single-expression

Merge-request: KT-MR-12035
Merged-by: Vladimir Sukharev <Vladimir.Sukharev@jetbrains.com>

compiler/testData/ir/irText/expressions/funInterface/samConversionsWithSmartCasts.fir.kt.txt

@@ -19,7 +19,9 @@ fun <T> test0(a: T) where T : KRunnable, T : Function0<Unit> {
 
 fun test1(a: Function0<Unit>) {
   when {
-    a is KRunnable -> run1(r = a /*as KRunnable */)
+    a is KRunnable -> { // BLOCK
+      run1(r = a /*as KRunnable */)
+    }
   }
 }
 
@@ -30,19 +32,25 @@ fun test2(a: KRunnable) {
 
 fun test3(a: Function0<Unit>) {
   when {
-    a is KRunnable -> run2(r1 = a /*as KRunnable */, r2 = a /*as KRunnable */)
+    a is KRunnable -> { // BLOCK
+      run2(r1 = a /*as KRunnable */, r2 = a /*as KRunnable */)
+    }
   }
 }
 
 fun test4(a: Function0<Unit>, b: Function0<Unit>) {
   when {
-    a is KRunnable -> run2(r1 = a /*as KRunnable */, r2 = b /*-> KRunnable */)
+    a is KRunnable -> { // BLOCK
+      run2(r1 = a /*as KRunnable */, r2 = b /*-> KRunnable */)
+    }
   }
 }
 
 fun test5(a: Any) {
   when {
-    a is KRunnable -> run1(r = a /*as KRunnable */)
+    a is KRunnable -> { // BLOCK
+      run1(r = a /*as KRunnable */)
+    }
   }
 }
 
@@ -89,3 +97,4 @@ fun test8(a: Function0<Unit>) {
 fun test9() {
   run1(r = ::test9 /*-> KRunnable */)
 }
+