This patch adds dartdoc to LazyBlock. Also, this patch fixes the scrolling
physics of LazyBlock. Previously, we updated a running simulation only when the
change in scroll behavior changed the current scroll offset. Now we update
running simulations every time the behavior changes because the simulation
might depend on quantities other than the current scroll offset.
* left -> leading (Removes an LTR bias)
* center -> title (Widget was actually centered)
* right -> actions (Removes an LTR bias, asymmetric with leading)
Fixes#2348
Most of the remaining widget examples are actually manual tests. This patch
moves them into //dev/manual_tests. A couple are examples of using services,
which I've moved to //examples/layers/services. The remainder are out-dated and
are removed by this patch.