[IR] Move IrFactory#createBlockBody overloads to extension methods

This is to prepare for IrFactory auto-generation (KT-59308).

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrFactory.kt

@@ -217,16 +217,4 @@ interface IrFactory {
         startOffset: Int,
         endOffset: Int,
     ): IrBlockBody
-
-    fun createBlockBody(
-        startOffset: Int,
-        endOffset: Int,
-        statements: List<IrStatement>,
-    ): IrBlockBody
-
-    fun createBlockBody(
-        startOffset: Int,
-        endOffset: Int,
-        initializer: IrBlockBody.() -> Unit,
-    ): IrBlockBody
 }

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrFactoryHelpers.kt

@@ -5,8 +5,22 @@
 
 package org.jetbrains.kotlin.ir.declarations
 
+import org.jetbrains.kotlin.ir.IrStatement
+import org.jetbrains.kotlin.ir.expressions.IrBlockBody
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrExpressionBody
 
 fun IrFactory.createExpressionBody(expression: IrExpression): IrExpressionBody =
-    createExpressionBody(expression.startOffset, expression.endOffset, expression)
+    createExpressionBody(expression.startOffset, expression.endOffset, expression)
+
+fun IrFactory.createBlockBody(
+    startOffset: Int,
+    endOffset: Int,
+    initializer: IrBlockBody.() -> Unit,
+): IrBlockBody = createBlockBody(startOffset, endOffset).apply(initializer)
+
+fun IrFactory.createBlockBody(
+    startOffset: Int,
+    endOffset: Int,
+    statements: List<IrStatement>,
+): IrBlockBody = createBlockBody(startOffset, endOffset) { this.statements.addAll(statements) }

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrFactoryImpl.kt

@@ -263,18 +263,4 @@ abstract class AbstractIrFactoryImpl : IrFactory {
         endOffset: Int,
     ): IrBlockBody =
         IrBlockBodyImpl(startOffset, endOffset)
-
-    override fun createBlockBody(
-        startOffset: Int,
-        endOffset: Int,
-        statements: List<IrStatement>,
-    ): IrBlockBody =
-        IrBlockBodyImpl(startOffset, endOffset, statements)
-
-    override fun createBlockBody(
-        startOffset: Int,
-        endOffset: Int,
-        initializer: IrBlockBody.() -> Unit,
-    ): IrBlockBody =
-        IrBlockBodyImpl(startOffset, endOffset, initializer)
 }

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrBlockBodyImpl.kt

@@ -20,7 +20,6 @@ import org.jetbrains.kotlin.ir.IrStatement
 import org.jetbrains.kotlin.ir.declarations.IrFactory
 import org.jetbrains.kotlin.ir.declarations.impl.IrFactoryImpl
 import org.jetbrains.kotlin.ir.expressions.IrBlockBody
-import org.jetbrains.kotlin.utils.SmartList
 
 class IrBlockBodyImpl(
     override val startOffset: Int,
@@ -30,10 +29,6 @@ class IrBlockBodyImpl(
         this.statements.addAll(statements)
     }
 
-    constructor(startOffset: Int, endOffset: Int, initializer: IrBlockBody.() -> Unit) : this(startOffset, endOffset) {
-        this.initializer()
-    }
-
     override val statements: MutableList<IrStatement> = ArrayList(2)
 
     override val factory: IrFactory