Rewrite the DevTools flame chart to snap to the selected tree branch

The DevTools flame chart currently supports W-A-S-D keys to zoom and pan. Some flame chart implementations, like Perfetto's CPU flame chart, do not support these gestures. Instead, clicking on a stack frame will "snap" the chart to that specific branch of the tree. From the selected node up, all stack frames are rendered as single-parent-single-child relationships, and then the selected nodes children are rendered as normal. To "zoom out" or navigate up the tree, you can select once of the currently selected node's ancestors.

_perfetto's CPU flame chart_

This would help some of the performance issues we have with the current CPU flame chart (e.g. https://github.com/flutter/devtools/issues/3876) and also simplify the code. This also would make the experience similar to other CPU flame chart tools users are used to using.

Start by locating the current DevTools CPU flame chart and its W-A-S-D zoom and pan handling. Compare its behavior with the described Perfetto CPU flame chart interaction; done means selecting a stack frame snaps to that branch, renders its ancestors as single-child paths, and allows navigating up by selecting an ancestor.

Vom Indexierungsmodell aus dem Issue-Text verfasst.