Replace urllib.request with urllib3 to support WebAssembly

[rpwagner]

As discussed in #2514, urllib.request is not supported in WebAssembly. This replaces urllib.request where needed with urllib3 which does work with WebAssembly. I've tried to keep the code changes to a minimum and to reuse existing semantic patterns.

The linter did introduce new lines in one of the imports. I found it odd but left it in place.

Rationale

This enables the use of Cartopy is Pyodide and JupyterLite. Without it, downloading of shape files, etc., fail. See #2514.

Implications

I've run the unit tests and nothing new fails. It's also been tested in JupyterLite and works. There is a chance that the download code path hasn't been fully tested and something may still need to be changed to support urllib3.

This also introduces a new dependency, even though urllib3 is widely available. It is also an existing package in Pyodide.

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[MMesch]

Is this PR still active? I am running into the same problem and would love to see a solution.

[greglucas]

It is still open, but needs a champion that is interested in merging it in. I'm not in favor of it because it adds a new dependency that seems somewhat unncessary except for a WASM environment, but I won't block if someone else thinks this is the way to go.

See the comment here and the thread for workarounds/suggestions on how to approach this: #2514 (comment)

[MMesch]

The workaround is reasonably easy and works for me. Thanks for pointing to it.

On the other hand, "except for a WASM environment" seems like a very good reason to me. Especially considering that WASM is a pretty universal standard these days rapidly gaining popularity through platforms such as JupyterLite. But I'm not neutral.

[dopplershift]

I've come around in favor of this approach for a few reasons:

• I'm interested in WASM
• We're already depending on requests conditionally through owslib
• urllib3 being a dependency of requests makes it 99% likely it's already installed in someone's environment and not a risky add.

I'll wait to merge a bit for any impassioned counterpoints, but IMO this is a reasonable merge.

[QuLogic]

Still needs the CLA to be signed, no opinion on the dependency myself.