Symfony version(s) affected: 4

Description
DateTimeType passes values in format yyyy-MM-dd'T'HH:mm:ssZ to the html5 input element. However chrome expects the format yyyy-MM-dd'T'HH:mm:ss for datetime-local input types.

How to reproduce

• Create a form with a DateTimeType child, widget = 'single_text'
• Pass data to the form
• Render the form in chrome (v66)
• An empty datetime input will be rendered

Possible Solution
When trying to set the format to DateTimeType::HTML5_FORMAT (yyyy-MM-dd'T'HH:mm:ss), the DateTimeType will automatically add the DateTimeToRfc3339Transformer viewTransformer which uses the format yyyy-MM-dd'T'HH:mm:ssZ.

• One solution would be make the use of DateTimeToRfc3339Transformer optional
• Another solution would be to get rid of the trailing Z in DateTimeToRfc3339Transformer, which would also be valid in RFC3339 I think.