Rename

• CardDemoType → CardType
• type → cardType

allowing DartPad code generator to better understand them.

Explanation

The DartPad code generator looks for all variables named type and replaces them with a specific demo type; for example, in material/dialog_demo.dart, the variable type always refer to the type of the demo we are running (one of alert, alertTitle, simple, fullscreen), so the code generator will replace type with DialogDemoType.alert, DialogDemoType.alertTitle, DialogDemoType.simple, and DialogDemoType.fullscreen in order to generate standalone apps for each demo type.

Since the type in material/cards_demo.dart refers to the type of the card we use, instead of the type of the demo, renaming it to cardType allows the code generator to avoid replacing them.