[NI] Add regression tests for builder inference

Actual fix is c02dd720
^KT-33542 Fixed
^KT-33544 Fixed
^KT-36446 Fixed

compiler/testData/codegen/box/inference/builderInferenceLeakingVariable.kt

@@ -0,0 +1,39 @@
+// Issues: KT-33542, KT-33544
+// WITH_RUNTIME
+// KJS_WITH_FULL_RUNTIME
+// IGNORE_BACKEND_FIR: JVM_IR
+// !LANGUAGE: +NewInference
+
+import kotlin.experimental.ExperimentalTypeInference
+
+interface In<in E> {
+    suspend fun send(element: E)
+}
+
+class InImpl<E>(val block: suspend In<E>.() -> Unit) : In<E> {
+    override suspend fun send(element: E) {}
+}
+
+@OptIn(ExperimentalTypeInference::class)
+public fun <T> builder(@BuilderInference block: suspend In<T>.() -> Unit) {
+    InImpl(block)
+}
+
+fun test33542() {
+    builder {
+        send(run {
+            15
+        })
+    }
+}
+
+fun test33544(){
+    builder {
+        send(run {
+            let { 0 } ?: 1
+            0
+        })
+    }
+}
+
+fun box() = "OK"