This reverts commit 55f9145e.

Turns out that this commit breaks apps that use the material library,
because of the _errorTextStyle DefaultTextStyle which has inherit:true.
Just setting it to false doesn't work, unfortunately, because then you
hit some sort of issue with merging that text style with others that
have inherit:true.

To make it clear that this constructor requires an explicit style. Also
throw a descriptive error recommending the inherit constructor for
styles with the inherit bit set.

Fixes #3842

Now past halfway though material.dart by files.

* justifyContent -> mainAxisAlignment
* alignItems -> crossAxisAlignment
* FlexJustifyContent -> MainAxisAlignment
* FlexAlignItems -> CrossAxisAlignment

Fixes #231

The terms "left" and "right" have an LTR bias. Instead, we now use
"leading" and "trailing", for these list and grid decorations so that
we can later rearrange them to match the reading order.

Fixes #2540
Fixes #2548

This patch renames StatelessComponent to StatelessWidget and
StatefulComponent to StatefulWidget.

Fixes #2308

Fixes #1382

This enum doesn't make sense anymore now that we can arbitrarily colorize
icons.  Instead, we just use a Color, which is both simpler and can be
interpolated during animations.

Fixes #1279