ENH: Add sort_columns parameter to combine_first

[U-S-jun]

• fixed BUG: combine_first reorders columns #60427
• [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.

This PR enhances the combine_first method in pandas.DataFrame by adding a new parameter, sort_columns, which allows users to control whether the result's column order should be sorted lexicographically or preserve the original order of the calling DataFrame (self).

Currently, combine_first always returns a DataFrame with columns sorted in lexicographical order, which may not be desirable for users who want to maintain the column order of the original DataFrame

df1 = pd.DataFrame({"B": [1, 2], "A": [3, 4]})
df2 = pd.DataFrame({"A": [5]}, index=[1])

result = df1.combine_first(df2)
# Current behavior:
#     A  B
# 0  3  1
# 1  4  2

With the new sort_columns parameter:

Default Behavior (sort_columns=True): Columns remain sorted as before.
New Behavior (sort_columns=False): Columns retain the order from the original DataFrame (self).

df1 = pd.DataFrame({"B": [1, 2], "A": [3, 4]})
df2 = pd.DataFrame({"A": [5]}, index=[1])

result = df1.combine_first(df2, sort_columns=False)
# New behavior:
#     B  A
# 0  1  3
# 1  2  4

Tests: Added new test cases in pandas/tests/frame/methods/test_combine_first.py to validate:
Default behavior with sort_columns=True.
Column order preservation with sort_columns=False.

Documentation:
Updated the docstring for combine_first with examples showcasing the new parameter.
Added a changelog entry in doc/source/whatsnew/v3.0.0.rst.

This enhancement maintains backward compatibility, as the default behavior (sort_columns=True) remains unchanged. The new parameter provides additional flexibility for users who need control over column order.

[rhshadrach]

While I'm positive on the linked issue, I'm negative on adding a keyword to sort the order of columns or not. I think it is a bugfix to change the behavior of pandas to preserve column order.

[rhshadrach]

Doesn't this drop columns if there are columns in other that aren't in self?