Normalize attrs using Tag.attributes_escape/1 from phoenix_html

[lnr0626]

the :attrs directive has some differences compared to passing attributes to content_tag based functions in phoenix ((e.g. link would convert phx_change to phx-change, and data: [thing: "value"] to data-thing="value"))

Adding a new type handler for html attributes to handle that behavior would address that inconsistency

[msaraiva]

You're right. We should try to follow the same rules.

[msaraiva]

@lnr0626 after this PR gets merged and we have a new version of phoenix_html released, we should change the implementation of :attrs and any other stuff we do in that regard to use the new Tag.attributes_escape/1. We'll probably need to preprocess a couple of our existing types before calling it but at least everything will work more consistently.