Applies media padding (e.g. iPhone X safe area insets) to the Material Design demos in the Gallery.
Covers the following demos:
* Buttons (via the TabbedComponentDemoScaffold change)
* Cards
* Expansion panels
* Grid list
* Icons
* Images (via the TabbedComponentDemoScaffold change)
* Page Selector
* Progress Indicator
* Scrollable tabs
* Selection controls (via the TabbedComponentDemoScaffold change)
* Snack bar
* Tabs
* Text fields
* Tooltips
Fixes#13594
Minor fixes throughout, e.g. removing trailing commas from the end of sample code expressions, changing headings to "sample code" more consistently, removing stale todos, fix typos in a private method name, minor grammar fixes, added some clarifications to CircularProgressIndicator, LinearProgressIndicator, CrossAxisAlignment, added some cross-references to various members, made it slightly clearer that layout algorithms are implementation details.
Clarified "elevation" throughout.
Added docs to InkResponse and InkWell.
Added sample code for: SliverAppBar, Card, ListTile, EdgeInsets, Row, Column, CustomScrollView, ListView, SliverFixedExtentList, and SliverGrid.
Fixes#10317.
Fixes#10316.
Fixes#10267. (sort of, see comment therein)
Fixes#9331. (sort of, see comment therein)
Fixes#9407. (sort of, see comment therein)
* Add cupertino to gallery and add CupertinoButto
* Use single quotes
* Add disabled state
* Some review notes
* Make button animation more responsive and tweak timing
* Renamed things Cupertino
* Button with background, move cupertino demos, move material demos
* Move 2 level list too
* Refactor various demo route names
* Some review notes
* More reviews and add test
* Linter as
* Move private constant up
