Defines opDispatch as two levels of nested templates, so that the outer level only checks the member name to match any member defined by one of the contained types. This allows hasMember!TA to report proper values instead of always assuming `true`.
As a side-effect, `isOutputRange!(TA, T)` now only returns true, if any of the contained types is actually a matching output range.
Before this change, the alignment of TaggedAlgebraic was always 4, which in turn had a 50% chance of aligning 8-byte pointers on a non-8-byte boundary, causing the pointer to become invisible to the GC (and less bad, causing performance degradation when dereferencing the pointer). This would happen in particular when the total size of the TaggedUnion/TaggedAlgebraic was not divisible by 8 and an array of values was built.
- Add constructors and assignment operators for unique types
- Rename field getters to fooValue and value!() to enable sane property syntax and to avoid confusion when modifying the returned reference
- Fix misnomer "isUnionType" instead of "isUnitType"
