Feature/new date picker tokens

[j-mnizhek]

Motivation and Context

We need styles for the second period on the calendar in the DatePicker component, so I've added three tokens:

• for the active start and end cells of the second period,
• their hover style,
• and border-color for range cells inside the second period.

I've also updated references for two date-picker tokens for better contrast, and added information about the comparison feature to the documentation.

Types of changes

• New feature (non-breaking change which adds functionality).
• Updated references for date-picker-cell-current tokens to increase contrast against background.

Checklist:

• My code follows the code style of this project.
• I have updated the documentation accordingly or it's not required.
• I have added changelog note to corresponding CHANGELOG.md file with planned publish date.