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.

Refactored formatter class #2359 which works with or without intl extension. Use PHP format patterns alsow with intl. Class is compatible with previous version.

Fixes #3687: Default `sourceLanguage` and `language` are now `en-US` in order for i18n formatter to work correctly

Adjustments code according to the standards.
Adding missing PHPDoc comment.

issue #2852