Support for placeholder in Dropdown

[victorfunes]

• [X] I have searched the Issues to see if this bug has already been reported
• [X] I have tested the latest version

Summary

Now the Dropdown has a placeholder property but it seems not being used. Does it make sense to enable it to be used when the label is not defined?

Maybe I am using it as a select incorrectly, but I don't like the style of the Select floating menu... If there is another way, any advise will be more than welcome.

Context

In case a dropdown label is initially not defined, it could show the placeholder. Now I am doing it from my components using:

<Dropdown label={label ?? placeholder} ...