[BUGFIX beta] Use properties before attributes

The HTMLBars attribute feature is less complicated if implemented as setting properties, and falling back to attributes if a property does not exist. This also allows some edge cases like booleans to Just Work for most cases (though they do not act like HTML in very rare edge cases).

There are minimal changed here to what goes live with beta, but it removes the current code's dependency on "quoted" being passed to the attribute hook for the new feature and cleans up a bunch of other code.

Also removes any caching by attribute name.

Of interest to folks might be the changes to tests, which indicate some interesting quirks.

/cc @mmun