* Wire up paragraph font weight and font style in canvas golden test

* Update TODOs in test

* Update goldens lock

The compositor expects the PaintContext's leaf_nodes_canvas to be non-null

* Include paragraph height in the top-level text style.

* Update test comment

* Update goldens lock

third_party/expat was recently migrated from flutter/buildroot to our
googlesource repo at https://flutter.googlesource.com/third_party/expat
in [1] and deleted from the buildroot in [2]. This rolls the buildroot
and adds the new upstream dependency.

[1] https://flutter-review.googlesource.com/c/third_party/expat/+/12700
[2] https://github.com/flutter/buildroot/pull/445

Bug: https://github.com/flutter/flutter/issues/39532

This picks up
https://flutter-review.googlesource.com/c/third_party/libpng/+/12660

Bug: https://github.com/flutter/flutter/issues/69221

Fix: add Android accessibility bounds offset when FlutterView's location is not left top corner (#25670)

https://dart.googlesource.com/sdk.git/+log/eff12d77a2ad..d05e7fc462ba

2021-04-20 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.14.0-18.0.dev
2021-04-19 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.14.0-17.0.dev
2021-04-19 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.14.0-16.0.dev
2021-04-19 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.14.0-15.0.dev
2021-04-19 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.14.0-14.0.dev
2021-04-19 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.14.0-13.0.dev
2021-04-18 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.14.0-12.0.dev
2021-04-18 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.14.0-11.0.dev
2021-04-17 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.14.0-10.0.dev
2021-04-17 dart-luci-ci-builder@dart-ci.iam.gserviceaccount.com Version 2.14.0-9.0.dev

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/dart-sdk-flutter-engine
Please CC dart-vm-team@google.com on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/master/autoroll/README.md

This reverts commit 8c14250f.