Following SERVER-90492, SolutionCacheData will be 8 bytes larger because a unique_ptr was added to allow for caching plans which use VirtualScanNodes. This facility is test only, so ideally, we wouldn't pay the cost of a larger struct in the general case.

As such, this ticket proposes converting SolutionCacheData to a variant. You can imagine:

• having one type for each type of data access plan (CollScan, Ixscan, or VirtualScan)
• Having one type for caching plans in production (collscan, ixscan) or for test only (virtual scan)