Made bigquery table schema diffsuppress func handle nested lists gracefully

[modular-magician]

Resolved #9230. The comparison function was assuming that if the current object was a list, it was the top-level schema list and could be sorted by field name. However, this logic ended up also getting applied to nested lists, which don't have a field name to sort by (thus causing a panic.)

Specifically, bigquery table schema can specify policyTags per-column.

I believe the purpose of sorting by field name is to prevent diffs if fields in the schema are reordered. We can preserve this logic by pre-sorting the schema by field name prior to passing it to the comparison function. (Note: due to nested fields, ended up going with a different strategy.)

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Release Note Template for Downstream PRs (will be copied)

bigquery: Fixed `google_bigquery_table.schema` handling of policyTags

Derived from GoogleCloudPlatform/magic-modules#4832

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