FIR2IR: wrap do-while loop in IrBlock

"so that variables declared in loop body are not visible outside of the
loop" (from commit d096f1d)

compiler/testData/ir/irText/expressions/whileDoWhile.fir.kt.txt

@@ -12,18 +12,24 @@ fun test() {
     x = <unary>.inc()
     <unary>
   }
-  do// COMPOSITE {
-  // }  while (less(arg0 = x, arg1 = 0))
-  do{ // BLOCK
+  { // BLOCK
+    do// COMPOSITE {
+    // }    while (less(arg0 = x, arg1 = 0))
+  }
+  { // BLOCK
+    do{ // BLOCK
+      val <unary>: Int = x
+      x = <unary>.inc()
+      <unary>
+    }    while (less(arg0 = x, arg1 = 15))
+  }
+  { // BLOCK
+    do// COMPOSITE {
     val <unary>: Int = x
     x = <unary>.inc()
     <unary>
-  }  while (less(arg0 = x, arg1 = 15))
-  do// COMPOSITE {
-  val <unary>: Int = x
-  x = <unary>.inc()
-  <unary>
-  // }  while (less(arg0 = x, arg1 = 20))
+    // }    while (less(arg0 = x, arg1 = 20))
+  }
 }
 
 fun testSmartcastInCondition() {
@@ -32,8 +38,10 @@ fun testSmartcastInCondition() {
     a is Boolean -> { // BLOCK
       while (a /*as Boolean */) { // BLOCK
       }
-      do// COMPOSITE {
-      // }      while (a /*as Boolean */)
+      { // BLOCK
+        do// COMPOSITE {
+        // }        while (a /*as Boolean */)
+      }
     }
   }
 }