fixes #5448

only method stubs so far

fixes #5683

close #5762

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

see http://derickrethans.nl/immutable-datetime.html
by @derickr

fixes #5179

close #5261

fixes #5260

related to #5128

related to #5214

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

use "just now" for empty time difference in Formatter.

fixed wrong language name definition

adding and reworking the conversion of:
- ICU to PHP
- PHP to ICU
- ICU to JUI
- PHP to JUI

This fix ensures the format configured in the formatter class is used in the message instead
of the default ICU format.

fixes #4960

ensure some features that were recently added to formatter keep working after refactoring

exclude parts that have different default values

Improved checks where substr_compare is used, replaced more substr + comapre cases with substr_compare

we do not want our own i18n database.
When this kind of data is needed intl extension is a requirement.