API: value_counts to consistently maintain order of input

[rhshadrach]

• closes BUG: GroupBy.value_counts doesn't preserve original order for non-grouping rows #59307 (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

Context is here: #59307 (comment)

[mroeschke]

+1 for this change. LGTM

[jorisvandenbossche]

(Just checked the whatsnew note)

[mroeschke]

Thanks @rhshadrach

[phofl]

This broke the following case:

df = pd.DataFrame({"a": [1, 2, 1, 2], "b": np.nan})
df.groupby("a").value_counts()

with

Traceback (most recent call last):
  File "/Users/patrick/Library/Application Support/JetBrains/PyCharm2024.1/scratches/scratch_1.py", line 100, in <module>
    df.groupby("a").value_counts()
  File "/Users/patrick/mambaforge/envs/dask-expr/lib/python3.12/site-packages/pandas/core/groupby/generic.py", line 2723, in value_counts
    return self._value_counts(subset, normalize, sort, ascending, dropna)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/patrick/mambaforge/envs/dask-expr/lib/python3.12/site-packages/pandas/core/groupby/groupby.py", line 2535, in _value_counts
    result_series = cast(Series, gb.size())
                                 ^^^^^^^^^
  File "/Users/patrick/mambaforge/envs/dask-expr/lib/python3.12/site-packages/pandas/core/groupby/groupby.py", line 2747, in size
    result = self._grouper.size()
             ^^^^^^^^^^^^^^^^^^^^
  File "/Users/patrick/mambaforge/envs/dask-expr/lib/python3.12/site-packages/pandas/core/groupby/ops.py", line 696, in size
    ids = self.ids
          ^^^^^^^^
  File "/Users/patrick/mambaforge/envs/dask-expr/lib/python3.12/site-packages/pandas/core/groupby/ops.py", line 750, in ids
    return self.result_index_and_ids[1]
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "properties.pyx", line 36, in pandas._libs.properties.CachedProperty.__get__
  File "/Users/patrick/mambaforge/envs/dask-expr/lib/python3.12/site-packages/pandas/core/groupby/ops.py", line 769, in result_index_and_ids
    result_index, ids = self._ob_index_and_ids(
                        ^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/patrick/mambaforge/envs/dask-expr/lib/python3.12/site-packages/pandas/core/groupby/ops.py", line 884, in _ob_index_and_ids
    ob_ids = np.where(ob_ids == -1, -1, index.take(ob_ids))
                                        ^^^^^^^^^^^^^^^^^^
IndexError: cannot do a non-empty take from an empty axes.