This commit allows to specify a deprecation level to a manual metadata
entry. The purpose of that new attribute is to distinguish cases where
the property is still bound (default) from cases where the property no
longer exists and won't be bound.
This gives the opportunity to IDEs to still show the property as an
error and offer documentation and an action to rename it if a
replacement exists.
Closes gh-9074
cdf5f6e0ee