Add constraints between two different stub variables instead of creating constraint error due to T1 isn't subtype of T2

^KT-44241 Fixed

compiler/testData/codegen/box/inference/builderInference/constraintsBetweenTwoStubVariables.kt

@@ -0,0 +1,25 @@
+// !LANGUAGE: +UnrestrictedBuilderInference
+// WITH_RUNTIME
+
+import kotlin.experimental.ExperimentalTypeInference
+
+class Foo<K11, K22>(val key: K11) {
+    fun emit1(key: K11) {}
+    fun get(): K11 = null as K11
+    fun emit2(key: K22) {}
+}
+
+@OptIn(ExperimentalTypeInference::class)
+fun <K1, K2> build(@kotlin.BuilderInference builder: Foo<K1, K2>.() -> Unit) {}
+
+fun run(x: Int) {
+    build {
+        emit1(x)
+        emit2(get()) // We shouldn't report type mismatch, instead we should add constraint StubTypeVariable(K2) >: StubTypeVariable(K1), then infer K2 into Int among K1
+    }
+}
+
+fun box(): String {
+    run(1)
+    return "OK"
+}