Fixed example of transactional operations in AR guide
Fixes #4813: Fixed MSSQL schema that was getting incorrect info about constraints
`yii\mongodb\Collection::buildLikeCondition()` fixed to be case insensitive.
Fixes typo in structure-assets.md
removes duplicated unnecessary sentence from structure-extensions.md
Merge pull request #4825 from nenad-zivkovic/master

[ci skip] Fixes typo in structure-assets.md
Fixes #4188: API exceptions are now exposing less data when YII_DEBUG is false

- If exception is internal it's always returned as HTTP 500 general purpose one.
- Type isn't exposed anymore.
Merge pull request #4826 from yiisoft/rest-dont-show-full-exceptions-in-production

Fixes #4188: API exceptions are now exposing less data when YII_DEBUG is false
Fixes #3283: Added `$checkAjax` to `yii\web\User::loginRequired()`