Clean up which directive attributes expect HTML vs C#

[danroth27]

Currently you need to specify a leading @ character for event handler values. For example:

<button @onclick="@IncrementCount">Count</button>

However, the leading @ character in the attribute value should not be required:

<button @onclick="IncrementCount">Count</button>

See the design notes in #6364

[danroth27]

@NTaylorMullen

[danroth27]

@rynowak It looks like this was the intended design for event handlers and bind, but what about directive attributes like @key and @bind:format?

[ajaybhargavb]

As of now,

• @ref, @bind, @bind-* etc all expect CSharp
• @bind:event, @bind:format, @key, and @onclick(and friends) all expect HTML

I understand we should fix @onclick to expect CSharp. Should anything else be different in the above list?

[NTaylorMullen]

Ehhh, I thought in Blazor this was all intentional. @rynowak / @SteveSandersonMS would know better though.

[rynowak]

I would expect bind:event and bind:format to expect HTML.

Key I'm not sure.

Others should be C#.

[ajaybhargavb]

I edited the list. I meant to put bind:event along with bind:format.