HtmlNode.ToString(): fix self-closing tags on empty non-void elements

[stroborobo]

Quoting from
https://www.w3.org/TR/2011/WD-html-markup-20110113/syntax.html#void-element

The following is a complete list of the void elements in HTML:
area, base, br, col, command, embed, hr, img, input, keygen, link,
meta, param, source, track, wbr

[...]

Void elements only have a start tag; end tags must not be specified
for void elements.
A non-void element must have an end tag, unless the subsection for
that element in the HTML elements section of this reference indicates
that its end tag can be omitted.

[stroborobo]

Hey 👋

Noticed that ToString'd script elements aren't getting their closing tag and that broke some HTML I glued together. This fixes it according to the spec.

I wasn't sure where to put isVoidElement since it's static data, please let me know if I should move it.

[stroborobo]

Also isVoidElement is a duplicate, just noticed while trying to fix another issue. (Dropped white space in text nodes)

https://github.com/fsprojects/FSharp.Data/blob/5a5f3e0/src/Html/HtmlParser.fs#L774

Private helper module at the start of the file?

[stroborobo]

Added tests

[cartermp]

Looks like FSharp.Data.Tests.HtmlParser.Renderes self-closing tag for void elements() is a failure here.

[stroborobo]

Oh right I fixed that locally and probably forgot to push again, will do once I'm at my desk again. Sorry, it's late 😅

[cartermp]

Approved with these changes and pending green CI

[cartermp]

Suggested change

	let ``Renderes self-closing tag for void elements``() =
	let ``Renders self-closing tag for void elements``() =

[cartermp]

Suggested change

	let ``Renderes no self-closing tag for non-void elements``() =
	let ``Renders no self-closing tag for non-void elements``() =

[stroborobo]

Sorry for the late response, typos are fixed now.

[cartermp]

Thank you!