Components: Build MDC-based button

[mmalerba]

Tasks

• [x] Scaffold empty classes, assets, demo, build config, etc.
• [x] Stub existing component API
• [x] Hook up MDC foundation and adapter
• [ ] Add remaining features on top of MDC implementation
• [ ] Test dark theme
• [ ] Test RTL
• [ ] Test with screen-readers
• [ ] Copy existing unit tests and ensure they all pass
• [ ] Copy existing e2e tests and ensure they all pass (if any)
• [ ] Verify SSR support in universal-app/
• [ ] Verify no size regression
• [ ] Create test harness
• [ ] Create schematics for migration
• [ ] Create user documentation

Additional notes

• Consider supporting button[mat-outlined-button]
• Should each button type have a unique top level class? e.g. mdc-mat-icon-button
• Consider if we want to add a "appearance/type" input to button, similar to form field (outline/stroked, flat, raised)

Breaking changes

Known issues & visual differences

• Disabled FAB does not look disabled
• Anchor button does not look disabled
• No focused state
• Icon buttons are not colored by theme
• Missing JSDoc comments on some exported symbols

[Suresh918]

@andrewseguin/@mmalarba What are these MDC based components... What is the difference between actual angular components and these? Can you please give the details..

[mmalerba]

These are versions of the same components we already have, with the same APIs, but based on top of the Material Design team's canonical implementation. They're not ready for use in applications yet which is why all of the code is currently under @angular/material-experimental.

[DaSchTour]

Hopefully this will also include buttons with leading icons?