This updates `AsyncSnapshot.data` to act as `AsyncSnapshot.requireData`
used to -- and it removes `AsyncSnapshot.requireData`. Correspondingly,
this adds a `StreamBuilder.withoutInitialData()` constructor, makes the
`initialData` argument to the default `StreamBuilder()` constructor required,
and deprecates the `initialData` argument to the `FutureBuilder()` constructor.
See the breaking change announcement for more info.
https://github.com/flutter/flutter/issues/34545https://groups.google.com/forum/#!topic/flutter-announce/H6Od0QdsdrI
* add trailing commas on list/map/parameters
* add trailing commas on Invocation with nb of arg>1
* add commas for widget containing widgets
* add trailing commas if instantiation contains trailing comma
* revert bad change
