reland fxbug.dev/94000: Set Opacity and Scale Flatland Values for Flatland Embedder

The PR https://github.com/flutter/engine/pull/36109 had to be reverted because it broke fuchsia tests.  Please reland it with the broken test fixed.

The broken test: https://ci.chromium.org/ui/p/flutter/builders/prod/Linux%20Fuchsia%20FEMU/11891/overview
The revert: https://github.com/flutter/engine/pull/36305