Previously, the client of PopupMenuButton needed to build all the menu times
when building the PopupMenuButton. This can get expensive if, for example, each
item in a scrollable list has a popup menu associated with it.
Now the client passes a builder function to the PopupMenuButton that gets
invoked only when its time to show the menu items.
* left -> leading (Removes an LTR bias)
* center -> title (Widget was actually centered)
* right -> actions (Removes an LTR bias, asymmetric with leading)
Fixes#2348
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#2540Fixes#2548
Rather than managing all the Material Design icons manually, we now
manage them using an icon font. The icon font contains glyphs for each
icon in an efficient vector format.
This patch updates the FLX tooling to include the MaterialIcons font and
updates the Icon widget to use the font instead of asset images.
Fixes#2313Fixes#2218Fixes#2009Fixes#994
