[FIX] web: make qwebjs tests pass again

A bunch of features had been added to the qweb test files and qwebjs
did not pass them as features were either implemented differently or
not implemented at all:

* Fixed wonky and not cross-impl tests
  - added ``not`` word replacemenet to qwebjs as I wasn't sure how to
    handle that one cross-impl
* fixed t-esc/t-raw to render content *inside* the host node e.g.
  span@t-esc should render as <span>{contents of esc}</span>
* added fallback to body content if t-esc/t-raw yields an empty result
* process t-att in order with t-att-* and t-attf-* rather than before
  them both
* suppress attribute generation entirely in case of falsy value