Add aliases for ImputeParams and TitleParams (#2732)

* Aliases for ImputeParams and TitleParams

Let's not merge this for a little while to make sure this doesn't break anything and to think about whether we need to do anything more sophisticated.  The point is to make it easier for `impute` and `title` to find the appropriate docstrings, as discussed in #2592

* Update altair/vegalite/v5/api.py

Co-authored-by: Joel Ostblom <joelostblom@users.noreply.github.com>

* Remove StackOffset alias

* Add a test related to aliases

Trying to ensure that we are not overwriting something defined on the Vega-Lite side when we define `Bin`, `Impute`, and `Title` in Altair.

* Update tests/vegalite/v5/tests/test_alias.py

Co-authored-by: Joel Ostblom <joelostblom@users.noreply.github.com>

* Update tests/vegalite/v5/tests/test_alias.py

Co-authored-by: Mattijn van Hoek <mattijn@gmail.com>

Co-authored-by: Joel Ostblom <joelostblom@users.noreply.github.com>
Co-authored-by: Mattijn van Hoek <mattijn@gmail.com>

altair/vegalite/v5/api.py

@@ -107,6 +107,8 @@ def _prepare_data(data, context=None):
 # ------------------------------------------------------------------------
 # Aliases & specializations
 Bin = core.BinParams
+Impute = core.ImputeParams
+Title = core.TitleParams
 
 
 @utils.use_signature(core.LookupData)

tests/vegalite/v5/tests/test_alias.py

@@ -0,0 +1,21 @@
+import pytest
+
+import altair.vegalite.v5 as alt
+
+
+def test_aliases():
+    """Ensure that any aliases defined in `api.py` aren't colliding with names already defined in `core.py` or `channels.py`."""
+    for alias in ["Bin", "Impute", "Title"]:
+        # this test pass if the alias can resolve to its real name
+        try:
+            getattr(alt, alias)
+        except AttributeError as e:
+            assert False, f"cannot resolve '{alias}':, {e}"
+
+        # this test fails if the alias match a colliding name in core
+        with pytest.raises(AttributeError):
+            getattr(alt.core, alias)
+
+        # this test fails if the alias match a colliding name in channels
+        with pytest.raises(AttributeError):
+            getattr(alt.channels, alias)