Generated.xcconfig is only required at build time for iOS apps. In the
flutter create project template and example apps, Generated.xcconfig was
previously marked as a resource to be bundled into the built app.

Eliminates 64-bit hardcoding for iOS test apps under dev/. This brings
them in line with the default iOS app templates.

* Revert "Revert engine (#13547)"

This reverts commit ee65db11.

* Keep flaky mark

* Revert "Include a directory with Flutter assets (#12944)"

This reverts commit 3af6b9cb.

* Revert "Upgrade project.pbxproj to include flutter_assets (#13011)"

This reverts commit 08128cb2.

* Revert "Upgrade complex_layout project.pbxproj to include flutter_assets (#13544)"

This reverts commit 35f1a041.

* mark complex_layout_ios__start_up as flaky

This consolidates all of the non-template .gitignore rules into the top level .gitignore, to ignore common things more broadly, with less maintenance needed for the .gitignore files. Does not touch the templates, so that they still produce needed .gitignores as part of flutter create.

Under android/ directory, ignore:
GeneratedPluginRegistrant.java

Under ios/ directory, ignore:
GeneratedPluginRegistrant.h
GeneratedPluginRegistrant.m
Pods/

* Update examples to lower the deployment target on iOS.

* Remove stray PRODUCT_BUNDLE_IDENTIFIER

This was erroneously added and overrides
the bundle for the gallery causing signing
to fail in my setup.

@chinmaygarde

* Remove PRODUCT_BUNDLE_IDENTIFIER from all Runner pbxproj's

We want to use the FlutterViewController in this new project template.

Fixes #4840

We now use a different approach for ios projects where the developer controls
the Xcode project file. This patch removes the old ".generated" approach in
favor of the new approach.

Initial version of complex layout performance test