fix: clamp displayed month when endMonth changes

[wanxiankai]

Summary

• Clamp the internally displayed month when navigation bounds change after mount.
• Keep dropdown captions and the month grid visible when a new endMonth falls before the current month.
• Add a regression test for issue Changing endMonth to a date smaller than the currently viewed month removes the month grid and dropdowns #2912.

Fixes #2912

Tests

• pnpm exec jest packages/react-day-picker/src/DayPicker.test.tsx --selectProjects src --runInBand --no-watchman
• pnpm run lint
• pnpm run typecheck
• TZ=UTC pnpm exec jest --selectProjects examples --selectProjects src --selectProjects packages --selectProjects scripts --runInBand --no-watchman

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[rodgobbi]

Hi @wanxiankai , thanks for the contribution! 🙏

But it's better to avoid useEffect, it's a common source of bugs with React.

Thanks to your PR I thought of a solution that doesn't rely on useEffect.
I'll prepare a PR to fix the issue and keep you posted. 👍

[gpbl]

Do we actually need to change this? Can't the date be controlled upstream? 🤔

[rodgobbi]

Do we actually need to change this? Can't the date be controlled upstream? 🤔

@gpbl but we would be forcing consumers to always control the month, and developer errors can still put the calendar in an unusable state.

I'm following your idea here #2671 (comment) to always make sure the calendar is in a usable state.