Python 2 has been end-of-life'd since January 2020, all Python scripts
on which Flutter depends have been migrated to Python 3. This changes
documentation and remaining invocations to explicitly invoke python3.

Issue: https://github.com/flutter/flutter/issues/83043

c0e59bc7b fix a typo in https://github.com/flutter/engine/pull/27311 (flutter/engine#27687) (#87763)

DataTable and Button NNBD docs fixes

f1a759d98 Roll Dart SDK from 5406f286f566 to 131d357297e2 (1 revision) (flutter/engine#27906) (#87726)

381d54e4c Roll Dart SDK from 96fdaff98f48 to 5406f286f566 (5 revisions) (flutter/engine#27903) (#87711)

This reverts commit 52bf9dbb.

This gesture recognizer can be used to recognize the classic
"onclick" behavior, where each tap in a series fires an event
with an incrementing "count" of how many taps have occurred
in series. This can in turn be used to build widgets that respond
to both tap and double-tap, or for widgets like the YouTube TV
player, where each subsequent tap in a series of >2 taps adjusts
the playhead another 15 seconds.

Fixes https://github.com/flutter/flutter/issues/81657