Fix structs_column_wrapper constructors to copy input column wrappers

[davidwendt]

Description

Fixes the cudf::test::structs_column_wrapper constructors that accept column_wrapper instances to copy the underlying column rather than move it. The constructor signatures do not provide any indication that the passed wrappers will be destroyed. Also, the other nested column wrapper constructors make copies unless the parameters are decorated with move declarations (i.e. &&).

Closes #13200

Checklist

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

[nvdbaranec]

This is great. There is a -lot- of test code out there that has to do some ugly code jiggling to get around this.

[vyasr]

This is great. There is a -lot- of test code out there that has to do some ugly code jiggling to get around this.

@nvdbaranec should we open an issue to track that cleanup? Not a high priority task, but it would be nice to know it could be done (I don't have the context for these tests but it sounds like you have some in mind?).

[davidwendt]

/merge