This PR adds the following lint rules to our list:
```
always_put_required_named_parameters_first
avoid_multiple_declarations_per_line
avoid_positional_boolean_parameters
avoid_returning_null_for_void
avoid_returning_this
avoid_unnecessary_containers
enable_null_safety
library_private_types_in_public_api
no_leading_underscores_for_library_prefixes
no_leading_underscores_for_local_identifiers
prefer_null_aware_method_calls
tighten_type_of_initializing_formals
unnecessary_late
use_setters_to_change_properties
```
And these rules were considered, and some changes were made according to
them as a clean-up, but in many places they didn't make sense
(`prefer_asserts_with_message` I would have included, but there were too
many places that needed to be changes):
```
collection_methods_unrelated_type
prefer_asserts_with_message
avoid_renaming_method_parameters
```
* Added Component.childrenFactory
* fix some of the lint warnings
* more lint warnings
* remove changelog entry
* more analyzer warnings
* one more warning
* one more warning
* remove more unused imports
* fix more warnings
* another warning
* one more warning
* a lot more warnings
* some more warnings
* fix warnings in flame_svg
* fix warnings in flame_bloc
* Remove OrderedSet override feature
* Remove testRandom change
* Remove unnecessary type checks
* Re-remove deprecated argument in random_test
Co-authored-by: Pasha Stetsenko <stpasha@google.com>
* Animations, CameraAndViewport, CollisionDetection and Components unified
* Added descriptions to effects
* Rename input games
* Unify input stories
* Add info to parallax section
* Added descriptions to the rendering examples
* Add descriptions to the sprites directory
* Fix utils and rendering section
* Add descriptions to the widgets section
* Delete directory that rebase brought back
* Unify game names
* Added some styleguide docs for examples
* Fix analyze issues
* All files should have _example as suffix
* Made the FollowComponentExample a bit easier to understand
* Change priority of ember
