Fixes #3535: Syntax changes

- Removed `form_begin`, `form_end`
- Added `use()` and `ViewRenderer::uses` that are importing classes and namespaces
- Added widget dynamic functions `*_begin`, `*_end`, `*_widget`, `widget_end`
- Added more tests
Fixes #3956: Flash messages set via `Yii::$app->session->setFlash()` will be removed only if they are accessed
Update a tip and an example

- add a tip that rbac.php is needed to create manually when using PhpManager.
- update that RbacController example needs to import Yii namespace.
Merge pull request #3983 from sitawit/patch-1

Update a tip and an example
Changed descriptive extension name to ID
Merge pull request #3978 from yiisoft/twig-syntax-changes

Fixes #3535: Syntax changes
added widget Breadcrumbs unit tests.
Fixes #3956: Debug toolbar was affecting flash message removal
Fixes #3979: Alert widget in advanced app is now able to display multiple flash messages of the same type
add translate
Merge pull request #3985 from githubjeka/translate-2

add guide-ru/rest-quick-start.md
Fixes #3793: Changed inline autocomplete hints style to get more IDEs support
doc improvement.
doc improvement [skip ci]
Merge upstream/master