Description

This PR makes it possible to interrupt an ongoing TabBarView animation.
Before this PR, when the TabBarView animation is running (after the user selected one tab in the tab bar), it is not possible to interrupt this animation. So if the user selects another tab, the TabBarView will first finish the ongoing animation and then starts the new one). Because the TabBar animation can be interrupted, this leads to TabBarView and TabBar animations being unsynchronized.

Before:

After:

Related Issue

Fixes #113020

Implementation choices

This PR combines several changes.

1. A refactoring to make the code more understandable.
2. _warpToIndex can be now called when there is already a warp underway, the new warp will interrupt the preceding one (This is the problem reported in TabController's index and animation is not working properly when a new tab is selected while there is a transition still occurring #113020).
3. A debatable choice was to make an aggressive simplification by removing the logic related to caching the children list (removal of _children and originalChildren). Recreating _childrenWithKey by calling ensureUniqueKeysForList seems to be cheap and less error-prone.

Tests

Adds 1 test.