[SPARK-50335][PYTHON][DOCS] Refine docstrings for window/aggregation functions - part 2

### What changes were proposed in this pull request?
Refine docstrings for window/aggregation functions:
1, make examples copy-pasteable;
2, specify the meaning of `str` input: either column name or literal string;
3, show both input and output columns;
4, add `see also` section for related functions;

### Why are the changes needed?
1, improve the documentation;
2, improve the doctest coverage;

### Does this PR introduce _any_ user-facing change?
doc changes

### How was this patch tested?
updated doctests

### Was this patch authored or co-authored using generative AI tooling?
no

Closes #48877 from zhengruifeng/py_doc_4.

Authored-by: Ruifeng Zheng <ruifengz@apache.org>
Signed-off-by: Hyukjin Kwon <gurwls223@apache.org>

Author: zhengruifeng