Fix: refactor to adapt to changes to shapely dependency

[chalmerlowe]

The shapely library has undergone some internal refactoring.
Certain classes, such as WKTReader are no longer used, instead, the library relies on some functions that are imported from what appears to be pygeos.

This change points at the correct function to replace the outdated method call.

• NEW: shapely.wkt.loads()
• OLD: shapely.geos.WKTReader(shapely.geos.lgeos).read

Fixes#1364 🦕

Context:

This issue appeared when running a test in python-bigquery-sqlalchemy ... when running certain tests in that library, the code tried to load the tests/unit/testconf.py file from that library which references table.py in this library.

That was causing some failures in tests in the python-bigquery-sqlalchemy library.

[chalmerlowe]

@shollyman can you take a look at this for me and give me a sanity check?

[shollyman]

I see in the pandas helper we also use the well-known bytes reader, does this also need cleanup?

https://github.com/googleapis/python-bigquery/blob/main/google/cloud/bigquery/_pandas_helpers.py#L66

May be also worth checking system tests for unusual setups.

Are there other imports under shapely that need scrutiny beyond shapely.geos?

[chalmerlowe]

@shollyman

I checked the remainder of the code for references to shapely, WKT*, WKB*, etc.

Added a minor change based on what I found.

[shollyman]

There's no test changes? Is this indicative that our existing tests were sufficient in catching and exercising this dependency? Do we need to exercise anything new as part of the changes?

[chalmerlowe]

There's no test changes? Is this indicative that our existing tests were sufficient in catching and exercising this dependency? Do we need to exercise anything new as part of the changes?

The existing tests were already using the new refactoring > they referred to the correct functions in the correct files.