"HTML Element" option for Columns and Columns blocks

[justintadlock]

Both the Columns and its inner Column block will often be used for structural sections on the page. Users/Themers should be able to set the HTML element used.

Currently, both blocks are wrapped in a <div>. However, <main>, <section>, <aside>, and <article> will make sense in various use cases.

<header> and <footer> could potentially make sense for the outer Columns block, but I'd like to focus on getting the other options in for sure.

[kraftner]

Related issues #15000 #27092

[carolinan]

I wonder if it would also make sense to move the HTML filter to its own separate control.
It is used but slightly differently for the group, template part and query blocks.