Support for 'multiple' attribute in '<select>' elements.

[MackinnonBuck]

Support for multiple attribute in <select> elements.
The onchange event will now provide an array of the selected elements via ChangeEventArgs when the multiple attribute is specified, and array values can be bound to the value attribute.

PR Description

• Added support for converting to/from array types in BindConverter.cs.
• Added special handling of <select> elements with type select-multiple in BrowserRenderer.ts.
• Updated the InputSelect component to infer the multiple attribute based on TValue.
• Added E2E tests.

Addresses #5519

[SteveSandersonMS]

This is looking excellent, and very close to being done now I think :)

[SteveSandersonMS]

@MackinnonBuck Again, this looks super and very close to being done :) I found one more thing that probably definitely needs attention, and a "maybe" thing. Hopefully that's the last of it!

[DamianEdwards]

This looks great! It would be amazing to get support for having a select element's items automatically populated with an Enum's values along with support for DisplayName for the text, when the select itself is bound to an Enum or IList<Enum> style property. It would make for a really compact and simple way to provide UX for enums, e.g.

<InputSelect @bind-Value="AThing">
</InputSelect>
<InputSelect @bind-Value="MultipleThings">
</InputSelect>
@code {
    Thing AThing;
    Thing[] MultipleThings;
    enum Thing
    {
        [DisplayName("This is the 1st thing")]
        FirstThing;
        [DisplayName("This is the 2nd thing")]
        SecondThing;
    }
}

If there's already an issue for this I couldn't find it! Happy to log one.

[SteveSandersonMS]

Awesome! Thanks so much for handling all the feedback. This looks like a really super and solid feature. Great to see you were able to eliminate the MultipleValues property too - this is a very clean API now!