Add tests for KT-20824, KT-23745, KT-23124, KT-20605, KT-23760

#KT-20824 Fixed
 #KT-23745 Fixed
 #KT-23124 Fixed
 #KT-20605 Fixed
 #KT-23760 Fixed

idea/testData/multiModuleHighlighting/multiplatform/useAppendable/a_common_dep(stdlib)/common.kt

@@ -0,0 +1,4 @@
+// KT-20824
+package foo
+
+fun <O : Appendable> O.appendMe(): O = this // kotlin.text.Appendable

idea/testData/multiModuleHighlighting/multiplatform/useAppendable/a_jvm_dep(stdlib)_dep(fulljdk)/jvm.kt

@@ -0,0 +1,7 @@
+package foo
+
+fun tryIt() {
+    buildString {  // kotlin.text.StringBuilder = java.lang.StringBuilder
+        appendMe()
+    }
+}