Improve the semantic structure of admin widgets.

[Antoliny]

Some of the widgets currently in the admin use <p> tags as their wrapper elements.

• ​Date Field
• ​Time Field
• ​DateTime Field
• ​URL Field

The current structure uses <p> tags, and for fields that can span multiple lines, such as DateTime and URL fields, <br> tags are used to provide visual line breaks.
Since <p> tags represent paragraphs, they are not suitable as wrappers for elements containing inputs, as is the case here. I believe this tag should be changed to a <div>.
Additionally, <br> tags are used for visual line breaks, but it would be more appropriate to remove them and implement the spacing using CSS.

[Antoliny]

​PR