Fix generic signature for SAM adapters and constructors

SAM-related code in codegen was using JavaClassDescriptor directly, which has
an erased signature. Create and use a new abstraction SamType which has a full
generic signature of a type which was used in the SAM construct

compiler/testData/codegen/boxWithJava/sam/adapters/genericSignature.java

@@ -0,0 +1,8 @@
+import java.util.Arrays;
+import java.util.Comparator;
+
+class JavaClass {
+    public static String foo(Comparator<String> comparator) {
+        return Arrays.toString(comparator.getClass().getGenericInterfaces());
+    }
+}

compiler/testData/codegen/boxWithJava/sam/adapters/genericSignature.kt

@@ -0,0 +1,5 @@
+fun box(): String {
+    val supertypes = JavaClass.foo { a, b -> a.compareTo(b) }
+    if (supertypes != "[java.util.Comparator<java.lang.String>]") return "Fail: $supertypes"
+    return "OK"
+}

compiler/testData/codegen/boxWithJava/sam/samConstructorGenericSignature.java

@@ -0,0 +1,9 @@
+class JavaClass {
+    interface Computable<T> {
+        T compute();
+    }
+
+    static <T> T compute(Computable<T> computable) {
+        return computable.compute();
+    }
+}

compiler/testData/codegen/boxWithJava/sam/samConstructorGenericSignature.kt

@@ -0,0 +1,8 @@
+import java.util.Arrays
+
+fun box(): String {
+    val r: JavaClass.Computable<String> = JavaClass.Computable { "OK" }
+    val supertypes = Arrays.toString(r.getClass().getGenericInterfaces())
+    if (supertypes != "[JavaClass.JavaClass\$Computable<java.lang.String>]") return "Fail: $supertypes"
+    return JavaClass.compute(r)!!
+}