Every `LowerType::visit*` function eventually calls through to a
`LowerType::handle*` function. After
https://github.com/swiftlang/swift/pull/81581, every
`LowerType::handle*` needs to set the `hasPack` flag based on the
passed-in type by calling `mergeHasPack`. Add the missing call in the
`handleAggregateByProperties` function.
rdar://152580661
