Fix tests to use Ahem, and helpful changes around that (#9332)

* Fix tests to use Ahem, and helpful changes around that

- Fix fonts that had metric-specific behaviours.

- LiveTestWidgetsFlutterBinding.allowAllFrames has been renamed
  to LiveTestWidgetsFlutterBinding.framePolicy.

- LiveTestWidgetsFlutterBinding now defaults to using a frame policy
  that pumps slightly more frames, to animate the pointer crosshairs.

- Added "flutter run --use-test-fonts" to enable Ahem on devices.

- Changed how idle() works to be more effective in live mode.

- Display the test name in live mode (unless ahem fonts are enabled).

- Added a toString to TextSelectionPoint.

- Style nit fixes.

* Roll engine to get Ahem changes.

* Update tests for dartdoc changes.

* Fix flutter_tools tests

packages/flutter_tools/lib/src/device.dart

diff --git a/packages/flutter_tools/lib/src/device.dart b/packages/flutter_tools/lib/src/device.dart
index a69951e..7489153 100644
--- a/packages/flutter_tools/lib/src/device.dart
+++ b/packages/flutter_tools/lib/src/device.dart
@@ -279,12 +279,14 @@
 class DebuggingOptions {
   DebuggingOptions.enabled(this.buildMode, {
     this.startPaused: false,
+    this.useTestFonts: false,
     this.observatoryPort,
     this.diagnosticPort
    }) : debuggingEnabled = true;
 
   DebuggingOptions.disabled(this.buildMode) :
     debuggingEnabled = false,
+    useTestFonts = false,
     startPaused = false,
     observatoryPort = null,
     diagnosticPort = null;
@@ -293,6 +295,7 @@
 
   final BuildMode buildMode;
   final bool startPaused;
+  final bool useTestFonts;
   final int observatoryPort;
   final int diagnosticPort;