Introducing Dateslider and DateRangeSlider

[slootsjj]

This PR introduces two date UI widgets. They combine native sliders with non-editable date pickers for day-level selection with consistent formatting and events.

New components

1. DateSlider — single-date selector with:

• Value (datetime) and ValueIndex (days-from-lower-limit) synchronization
• Limits (datetime[2]) with start-of-day normalization
• DisplayFormat passthrough to both slider tick labels and date picker
• Optional Orientation (horizontal/vertical) and DatepickerSize
• Events: ValueChanged, ValueChanging, LimitsChanged

2. DateRangeSlider — two-date range selector with:

• Value (datetime[2]) and ValueIndex (days-from-lower-limit) synchronization
• Limits (datetime[2]) with start-of-day normalization
• MinGap (enforces minimum days between start/end)
• DisplayFormat, Orientation, DatepickerSize
• Events: ValueChanged, ValueChanging, LimitsChanged
• Note: Compatible with MATLAB R2024b or higher.

UX & behavior
Tick labels auto-scale from limits using the chosen DisplayFormat
Arrow buttons step by property Step (a calendarDuration) and auto-disable at bounds

Additional note

• The TickableDateSlider mixin class was introduced to support these widgets.
• The icons up_grey_12.png and down_grey_12.png were added to support these widgets.
• WidgetsList.mlx was updated to include these widgets.

Rationale
Provides a consistent, accessible way to pick single dates or ranges with clear ticks, bounded interactions, and unified events.

[rjackey]

@slootsjj thank you for your contribution and my apologies I've not had a chance to review yet. It is still on my task list and I hopefully will have some time in a couple weeks.

[rjackey]

@slootsjj these are nice contributions, thank you!

In testing these out I am getting an issue with onSliderChanging of DateRangeSlider when dragging.

It seems the round() might put the date outside the limits?

  Error using matlab.ui.control.DatePicker/set.Value (line 148)
  'Value' must be a finite datetime object within the range of 'Limits' or NaT.
  
  Error in wt.DateRangeSlider/onSliderChanging (line 452)
              obj.DatepickerLeft.Value = changedDate(1);
              ^^^^^^^^^^^^^^^^^^^^^^^^
  Error in wt.DateRangeSlider>@(h,e)obj.onSliderChanging(e) (line 274)
              obj.Slider.ValueChangingFcn = @(h,e)obj.onSliderChanging(e);

Also just a note if you like you can add app designer metadata, or I can try to do so later.