GH-43985: [Python][C++] Fixed pyarrow table equality function not comparing table data when comparing against itself

[Yimche]

Rationale for this change

This change is to address issue #43985 in which a bug in the behaviour of equality on pyarrow tables occurs when comparing a table containing a NaN value against itself.

What changes are included in this PR?

• Removed if block in arrow/cpp/src/arrow/table.cc that forced a return true if memory address of the two items being compared were equal, no matter the data stored inside.
• Added test case.

Are these changes tested?

Yes. I put a test in the arrow/python/pyarrow/tests/test_table.py under the test_table_from_pydict function, as I wasn't sure and couldn't find where else to put the test.

Are there any user-facing changes?

No

• GitHub Issue: #43985