[PSI2IR] Support context receivers on classes

compiler/testData/codegen/box/extensionClasses/generics.kt

@@ -0,0 +1,10 @@
+// TARGET_BACKEND: JVM_IR
+// IGNORE_BACKEND_FIR: JVM_IR
+
+context(T) class B<T : CharSequence> {
+    val result = if (length == 2) "OK" else "fail"
+}
+
+fun box() = with("OK") {
+    B().result
+}