[Checkbox] use standard values for checked attribute

[rtritto]

For checked attribute, instead of value ("checked" | undefined):

<input type="checkbox" checked="checked" class="checkbox" />
---
<input type="checkbox" class="checkbox" />

use the standard values (boolean | undefined):

<input type="checkbox" checked class="checkbox" />
---
<input type="checkbox" checked={false} class="checkbox" />
OR
<input type="checkbox" class="checkbox" />

[saadeghi]

https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#boolean-attributes

The values "true" and "false" are not allowed on boolean attributes.

Here is an example of a checkbox that is checked and disabled. The checked and disabled attributes are the boolean attributes.

<label><input type=checkbox checked name=cheese disabled> Cheese</label>

This could be equivalently written as this:

<label><input type=checkbox checked=checked name=cheese disabled=disabled> Cheese</label>

You can also mix styles; the following is still equivalent:

<label><input type='checkbox' checked name=cheese disabled=""> Cheese</label>

[rtritto]

I was confused in JSX with:

<input type="checkbox" checked="checked" class="checkbox" />

because I got:

Type 'string' is not assignable to type 'boolean | undefined'.ts(2322)
jsx.d.ts(911, 5): The expected type comes from property 'checked' which is declared here on type 'InputHTMLAttributes<HTMLInputElement>'
(property) JSX.InputHTMLAttributes<HTMLInputElement>.checked?: boolean | undefined

Anyway I resolved using boolena value, thanks!