Revert longPress/Tap and Gallery changes

* Revert "New Flutter Gallery UI (#16936)"

This reverts commit 7038597b.

A new front-end for the Flutter Gallery example.

* Gallery scaffolding

* Started RenderSliver

* demo and initial hookup

* Cleaned up demo more and scaffolding basic sliver->widget communication structure.

* works

* states and default indicator building works

* start adding docs

* added an alignment setting optimized the sliver relayout mechanism

* tested a default bottom aligned sized indicator

* Added a bunch of tests

* more fixes and more tests

* Finished the tests

* Add docs

* Add more doc diffing wrt material pull to refresh

* Mention nav bar synergy

* add more asserts

* review 1

* Fix mockito 2 / dart 2 / strong typed tests

* review

* Remove the vscode config

* review

* spelling: accommodate

* spelling: allotted

* spelling: anonymous

* spelling: artificial

* spelling: associated

* spelling: asset

* spelling: button

* spelling: canvas

* spelling: compatibility

* spelling: coverage

* spelling: condition

* spelling: decoration

* spelling: deferring

* spelling: diameter

* spelling: direction

* spelling: displacement

* spelling: dropdown

* spelling: needing

* spelling: environment

* spelling: exited

* spelling: expansion

* spelling: explore

* spelling: families

* spelling: horizontal

* spelling: increment

* spelling: indices

* spelling: internationalization

* spelling: labrador

* spelling: localizations

* spelling: midflight

* spelling: milliseconds

* spelling: minimum

* spelling: multiple

* spelling: multiplication

* spelling: navigator

* spelling: overridden

* spelling: package

* spelling: performance

* spelling: platform

* spelling: porsche

* spelling: position

* spelling: preceded

* spelling: precede

* spelling: precedence

* spelling: print

* spelling: property

* spelling: readily

* spelling: reproducibility

* spelling: rounded

* spelling: scroll

* spelling: separate

* spelling: separator

* spelling: services

* spelling: specific

* spelling: specify

* spelling: synchronously

* spelling: through

* spelling: timeout

* spelling: triangle

* spelling: trivial

* spelling: unusual

* spelling: then

* spelling: vertically

* spelling: visible

* spelling: visited

* spelling: voice

* controller, position and test

* Make controllers swappable

* WIP

* Create a ListWheelScrollPhysics

* Created picker and gallery demo and testing now

* Works. Ready to document and test.

* Document and add tests. Make the scroll controller more generic.

* minor cleanup

* review

* review

* fix tests

* stop using TransformLayers for now

In https://github.com/flutter/flutter/pull/13141 I updated the demo name
from 'Animated Images' to 'Animated images' before submitted, but did
not update the name in the smoketest and transitions_perf test.

* Built first tab

* Small additions

* started tab 3

* Need color arithmetics

* tab 2 built

* finalize

* lint and tests

* review

* Reapply docs after rebase

* use color.computeLuminance

* linter

* nit

package:test does not allow main() methods to have required
arguments - changing to an optional positional arguments list
fixes this.

* Benchmark for semantic overhead during transitions

* review comments

Also refactors demos list into a class with `synchronized` and
`profiled` properties.

When run with --trace-startup, as we do in this test, the VM stores
trace events in an endless buffer instead of a ring buffer. To avoid
out-of-memory conditions, we restrict timeline collection to a subset.

Fixes https://github.com/flutter/flutter/issues/5935

...now that we have generic methods, their types need to be specified too.

With frameSync enabled, flutter_driver actions will only be performed
when there are no pending frames in the app under test. This helps with
reducing flakiness.