Fix split-record result list column offset type

[davidwendt]

Description

Fixes offsets type for list column returned by cudf::strings::split_record and cudf::strings::split_record_re when large-strings enabled. The list column offsets type must be INT32. The code was changed to use the appropriate make_offsets_child_column utility function.
Also added some is_large_strings_enabled() checks to check-overflow gtests.
This allows all current gtests to pass when the large-strings support environment variable is set.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[davidwendt]

/merge