Fixes to the byte_operator lowering unit test [blocks: #2068, #4062, #4063]

[tautschnig]

Let's only test byte extracts within bounds for now (there is ample work to be
done to get those right), but make sure there is possible combination for each
pair of types. Endianness needs to be taken into account when constructing the
expected value. Disable any non-POD tests as they all need more work.

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• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
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[allredj]

✔️
Passed Diffblue compatibility checks (cbmc commit: f1795cb).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/99573209

[allredj]

✔️
Passed Diffblue compatibility checks (cbmc commit: a8c5ee0).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/99647141

[allredj]

✔️
Passed Diffblue compatibility checks (cbmc commit: 2467571).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/99708859