fix(ui5-date-range-picker): remove only portrait mode on calendars when two months are shown

[GDamyanov]

Summary

Fixes two-month Calendar behavior by using orientation (_portraitView) only for header/button layout decisions, instead of mixing in compact density logic.

What was changed

• Removed compact mode dependency from two-month layout checks in Calendar.ts.
• Updated multi-month header rendering conditions in CalendarTemplate.tsx.
• Updated next-button visibility logic in CalendarHeaderTemplate.tsx.
• Improved popup viewport behavior in Calendar.css by adding:
  • overflow: auto;
  • max-height: calc(100vh - 3rem);

Result

• Correct header and navigation behavior in two-month mode.
• Consistent behavior across cozy and compact densities.
• Better usability in smaller viewports (prevents clipping by allowing scroll).

[sap-ui5-webcomponents-release]

🚀 Deployed on https://pr-13703--ui5-webcomponents-preview.netlify.app