compiler: disallow generic method receiver

Either non-pointer or pointer, both cases are disallowed to be generic.
Need to be reverted and properly handled within the scope of #2376.

Signed-off-by: Anna Shaleva <shaleva.ann@nspcc.ru>

pkg/compiler/generics_test.go

@@ -0,0 +1,38 @@
+package compiler_test
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/nspcc-dev/neo-go/pkg/compiler"
+	"github.com/stretchr/testify/require"
+)
+
+func TestGenericMethodReceiver(t *testing.T) {
+	t.Run("star expression", func(t *testing.T) {
+		src := `
+		package receiver
+		type Pointer[T any] struct {
+			value T
+		}
+		func (x *Pointer[T]) Load() *T {
+			return &x.value
+		}
+`
+		_, _, err := compiler.CompileWithOptions("foo.go", strings.NewReader(src), nil)
+		require.ErrorIs(t, err, compiler.ErrGenericsUnsuppored)
+	})
+	t.Run("ident expression", func(t *testing.T) {
+		src := `
+		package receiver
+		type Pointer[T any] struct {
+			value T
+		}
+		func (x Pointer[T]) Load() *T {
+			return &x.value
+		}
+`
+		_, _, err := compiler.CompileWithOptions("foo.go", strings.NewReader(src), nil)
+		require.ErrorIs(t, err, compiler.ErrGenericsUnsuppored)
+	})
+}