fixes #5601

also enhance test README

Fixed `yii\console\controllers\AssetController` breaks CSS URLs in case target file localed at `yii\web\AssetManager::basePath` root

Fixes #5467: Added ability to pass HTML tag options to `asEmail()`, `asImage()` and `asUrl()` methods of `yii\i18n\Formatter`

Additional check added to `yiiunit\extensions\authclient\BaseClientTest::testNormalizeUserAttributes()`

Added ability to operate nested and complex attributes via `yii\authclient\BaseClient::normalizeUserAttributeMap`

Fixes #5316: Added `startsWith()` and `endsWith()` to `yii\helpers\StringHelper`. Methods are binary-safe, multibyte-safe and optionally case-insensitive

fixes #5179

fixes #5331

close #5261

related to #5128

Fixes #3197: Using `ActiveQuery::indexBy()` may cause relational AR queries to generate incorrect relational results

feature is not reliable

fixes #5136

fixes #4989

Enhances `normalizeDateTimeValue` to return a DateTime object instead of a converted double value, that fails. The DateTime object input is supported by 32 bit, 64 bit, as well as the `IntlDateFormatter` to format all years. (including fixing of the Y2K38 bug). Fixes issue in #4989.

close #5000

Fixes #3725: Fixed the bug that the filtering condition used in relation definition was ignored when calling `ActiveRecord::unlinkAll()`

asArray will not include null valued keys