ninja_base: Introduce a ninja bbclass

For now, it only handles the depndency to ninja-native and handling the
export of the MAXLOAD_NINJA variable.

Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>

meta-oniro-staging/classes/ninja.bbclass

+# SPDX-FileCopyrightText: Huawei Inc.
+#
+# SPDX-License-Identifier: Apache-2.0
+
+DEPENDS:prepend = "ninja-native "
+
+MAXLOAD_NINJA ??= "0"
+export MAXLOAD_NINJA