feat: Add deprecated attribute and is_deprecated property to obje…

…cts/aliases

src/griffe/dataclasses.py

@@ -400,6 +400,9 @@ def __init__(
         self.public: bool | None = None
         """Whether this object is public."""
 
+        self.deprecated: str | None = None
+        """Whether this object is deprecated (boolean or deprecation message)."""
+
         self._lines_collection: LinesCollection | None = lines_collection
         self._modules_collection: ModulesCollection | None = modules_collection
 
@@ -852,6 +855,9 @@ def __init__(
         self.public: bool | None = None
         """Whether this alias is public."""
 
+        self.deprecated: str | bool | None = None
+        """Whether this alias is deprecated (boolean or deprecation message)."""
+
         self._parent: Module | Class | Alias | None = parent
         self._passed_through: bool = False
 

src/griffe/mixins.py

@@ -434,6 +434,12 @@ def is_public(self) -> bool:
         # If we reached this point, the object is public.
         return _True  # type: ignore[return-value]
 
+    @property
+    def is_deprecated(self) -> bool:
+        """Whether this object is deprecated."""
+        # NOTE: We might want to add more ways to detect deprecations in the future.
+        return bool(self.deprecated)  # type: ignore[attr-defined]
+
 
 # This is used to allow the `is_public` property to be "callable",
 # for backward compatibility with the previous implementation.