Add JS.Verbatim and JS.Html helpers

[Jand42]

To allow printing any code fragments directly (unchecked) to .js output, also html fragments for .jsx. You can only use constant strings or interpolated strings as argument.

   JS.Verbatim $"console.log({x})" // translated to: `(console.log(x))`
   JS.Html $"<div>{x}</div>" // translated to: `(<div>{x}</div>)`

[granicz]

Also, when translating placeholders like:

<{QRCode} message={value} size="0.5"></{QRCode}>

... omit the {}'s from around QRCode, because we can detect that <{...}> and </{...}> placeholders yield custom element names.

[granicz]

I really find the name JS.Html confusing - since it's a trigger to generate .jsx, I'd rename it to something more explicit such as JS.jsx. One bonus is that when renamed properly, it also becomes compatible with vscode-template-fsharp-hightlight.

[Jooseppi12]

Added a JS.Jsx function that is equivalent of the JS.Html function and exposed lowercase variants of those two.