Prohibit using null as a value of generic type

#KT-7350 Fixed
 #KT-7736 Fixed
 #KT-7485 Fixed

compiler/testData/diagnostics/tests/generics/nullability/nullToGeneric.kt

@@ -0,0 +1,35 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER,-UNUSED_VARIABLE,-BASE_WITH_NULLABLE_UPPER_BOUND
+
+fun <E> bar(x: E) {}
+
+fun <T> foo(): T {
+    val x1: T = <!NULL_FOR_NONNULL_TYPE!>null<!>
+    val x2: T? = null
+
+    bar<T>(<!NULL_FOR_NONNULL_TYPE!>null<!>)
+    bar<T?>(null)
+
+    return <!NULL_FOR_NONNULL_TYPE!>null<!>
+}
+
+fun <T> baz(): T? = null
+
+fun <T> foobar(): T = <!NULL_FOR_NONNULL_TYPE!>null<!>
+
+class A<F> {
+    fun xyz(x: F) {}
+
+    fun foo(): F {
+        val x1: F = <!NULL_FOR_NONNULL_TYPE!>null<!>
+        val x2: F? = null
+
+        xyz(<!NULL_FOR_NONNULL_TYPE!>null<!>)
+        bar<F?>(null)
+
+        return <!NULL_FOR_NONNULL_TYPE!>null<!>
+    }
+
+    fun baz(): F? = null
+
+    fun foobar(): F = <!NULL_FOR_NONNULL_TYPE!>null<!>
+}

compiler/testData/diagnostics/tests/generics/nullability/nullToGeneric.txt

@@ -0,0 +1,17 @@
+package
+
+internal fun </*0*/ E> bar(/*0*/ x: E): kotlin.Unit
+internal fun </*0*/ T> baz(): T?
+internal fun </*0*/ T> foo(): T
+internal fun </*0*/ T> foobar(): T
+
+internal final class A</*0*/ F> {
+    public constructor A</*0*/ F>()
+    internal final fun baz(): F?
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    internal final fun foo(): F
+    internal final fun foobar(): F
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    internal final fun xyz(/*0*/ x: F): kotlin.Unit
+}