Revert longPress/Tap and Gallery changes

* Give more room for the front layer drag on iPhone X

* Tweak the animation visual effects

* review lint

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

This reverts commit 7038597b.

A new front-end for the Flutter Gallery example.

Semantics object support for edge triggered semantics 

This chip demo is more interactive than the last one, trying to exercise all of the types of chips for a demo that lets you select different types of "chips" (like tortilla, wood, micro, etc.), and then filter them and select an action on them.

Changes since last roll:
```
ed303c628 Roll dart sdk again. Previous roll required 23ae4fa098 revert. (#4966)
8cd272733 Revert "Roll dart to 7764e6962e22afcf4b58c4e3cef3147330f3c884. (#4960)" (#4965)
9199b40f2 Revert "Support multiple shells in a single process. (#4932)" (#4964)
6baff4c82 Support multiple shells in a single process. (#4932)
31c5bb427 Roll dart to 7764e6962e22afcf4b58c4e3cef3147330f3c884. (#4960)
c8e4c6984 Avoid copying the contents of large platform message responses (#4947)
5ff527295 Update to use new vulkan GrBackendRenderTarget ctor. (#4962)
0c8993a1a Update to use new vulkan GrBackendRenderTarget ctor (part 2) (#4963)
132ebdda8 Revert "Roll src/third_party/skia/ 9874bf1bc..52e16d984 (135 commits) (#4958)" (#4961)
11882ab9e Roll src/third_party/skia/ 9874bf1bc..52e16d984 (135 commits) (#4958)
```

Add consts

Make the full-screen dialog text editable in gallery (#13690)

* Remove explicit child nodes

* Remove semantics on no-op menu buttons

* Add a dummy action to the overflow bar

* Add disable Cupertino Switch example

* keep trailing commas consistent

* fix Cupertino Switch example linter error

* Added BottomAppBar docked FloationActionButtonLocations

* Moved the startTop FloatingActionButtonLocation to the demo

* fixed a typo