- #3386
- initialize comparison `HashSet` with unencoded values to ensure both are checked
- address perf and correctness issues in this code
- `context.Items[typeof(SelectTagHelper)]` entry read as `ICollection` but written as `IReadOnlyCollection`
- `IReadOnlyCollection` worse because it does not include `Contains()`, causing Linq use
- every `<option>` element recalculated the encoded values and created a `HashSet` to contain them
- add `CurrentValues` type to cache this `HashSet` in `context.Items`
- each `OptionTagHelper` created the additional `HashSet` even if `Value` was bound
fa8c2eac3e