meta-java: Add dynamic layer for staging changes to meta-java recipes

We don't use meta-java in OHOS, and are re-using meta-ohos-staging in
meta-openharmony, which does use meta-java.
So in order to allow staging changes to meta-java recipes, we need this
dynamic layer to avoid breaking OHOS.

Signed-off-by: Esben Haabendal <esben.haabendal@huawei.com>