Move Html module to a separate assembly with all inlines

[Tarmil]

Blazor's tree shaking only shrinks System.* and Microsoft.* assemblies; other assemblies, including Bolero.*, are either served whole, or omitted if they're not called at all. As a consequence, all the functions for HTML elements, attributes, event handlers and binders are served, even though any given project only uses a fraction of them.

We could improve this by moving these functions to a separate assembly and making them all inlines. Since they're all inline, no actual code from the new assembly is called, so this assembly is omitted entirely from the output. Based on a quick experiment, the resulting download size for a small application is reduced by about 40kB (uncompressed).

This would also make alternative syntax ideas such as #167 more appealing, as their download size wouldn't be burdened by the default Html module at all.

[Tarmil]

Closed by #169.