Matan Lurey 8a55ee5d07 Add a DlStopwatchVisualizer and conditionally use it for Impeller (flutter/engine#45259) ...

Closes https://github.com/flutter/flutter/issues/126009.

One major change, as-per @jonahwilliams's feedback, is that I created a helper class called `DlVertexPainter`, which provides a `DrawRect`-like API, but just builds a buffer of vertices, resulting into just a single:

```cc
// Actually draw.
canvas->DrawVertices(painter.IntoVertices(), DlBlendMode::kSrc, paint);
```

Also, added test for it, since there is no way to screenshot test to Impeller overlay yet.

# Impeller

![Screenshot 2023-08-30 at 2 08 51 PM](https://github.com/flutter/engine/assets/168174/13bb83a7-9a02-40ae-b9e4-d71a2e47b594)

2023-08-30 23:15:16 +00:00

..

src/flutter

Add a DlStopwatchVisualizer and conditionally use it for Impeller (flutter/engine#45259)

2023-08-30 23:15:16 +00:00