Fixes https://github.com/flutter/flutter/issues/6734

Fonts should never be bundled on Fuchsia.

People get confused by the tight constraints.

Based on P5's experience

Fixes https://github.com/flutter/flutter/issues/6628

Closes https://github.com/flutter/flutter/issues/5781

I think we must have accidentally checked this in some time.

Closes https://github.com/flutter/flutter/issues/6125

Closes https://github.com/flutter/flutter/issues/6141

Closes https://github.com/flutter/flutter/issues/5743

Closes https://github.com/flutter/flutter/issues/5617

* make showElapsedTime default to true

* support nested progresses

* improve hot reload message

* rethrow

- [x] Remove the second full-sync on startup.
- [x] Always invoke the snapshotter to determine the minimal set of Dart sources used.
- [x] Only synchronize the *used* Dart sources to DevFS.
- [x] Detect syntax / file missing errors on the host and gate reloads / restarts.

On Android and Fuchsia, default to Roboto. On iOS, use San Francisco.

This is causing issues when integratting Flutter into GN as the
generated depfile refers to snapshot as the target instead of the
bundle. We instead use a separate GN action to generate the
snapshot use the Flutter compiler to only assemble the bundle.

* add flutter run --machine flag
* refactor daemon stdin/out command stream/response
* extract daemon startApp method
* refactor flutter run --machine to call daemon.startApp