Separate date and datetime options in date picker control

[GeoSander]

Description

This PR breaks the "Date or date time" option in the DatePickerDirective.js into 2 separate options:

• Date (only)
• Date and time

Date (only) will be the default option when creating new records.
For existing records, if there's a time component (and hideTimeInCalendar is not set), it will show date and time first.

Furthermore, the directive has been cleaned up and refactored a bit, and the CSS simplified (using flex). The HTML dropdown contains an additional option (if hideTimeInCalendar is false) and 2 new translation keys (dateOnlyMode and dateTimeMode) so there will not be any conflicts with the old dropdown translations for older versions.
The calendar icon was changed to a cog icon to make clear that it's a config option and to make sure that it cannot be confused for the other calendar icon in the date field.

Please read issue #9152 for more context.

Checklist

• I have read the contribution guidelines
• Pull request provided for main branch, backports managed with label
• Good housekeeping of code, cleaning up comments, tests, and documentation
• Clean commit history broken into understandable chucks, avoiding big commits with hundreds of files, cautious of reformatting and whitespace changes
• Clean commit messages, longer verbose messages are encouraged
• API Changes are identified in commit messages
• Testing provided for features or enhancements using [automatic tests](https://github.com/geonetwork/core-geonetwork/blob/main/software_development/TESTING.md)
• User documentation provided for new features or enhancements in manual
• Build documentation provided for development instructions in README.md files
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[josegar74]

@GeoSander I have done this test:

1. Create a new ISO19139 metadata, and set a date.

2. Save the metadata --> the form shows the date properly

3. Change to datetime and set the time.

4. Save the metadata --> the form shows the datetime properly

5. Change to date and save the metadata --> the form shows the datetime instead of the date

[GeoSander]

Thanks for the review @josegar74, I fixed ES5 compatibility (and adjusted my IDE to skip ES6 inspections).
I will also do some more tests now switching between modes and saving the metadata, to see if I can make that more robust.