Add multiple months visual selection

[luistorres]

Description

Currently there's a selectsMultiple flag that enables the pick of multiple dates, yet the selection styles for when applied together with showMonthYearPicker was never implemented.

Problem Current behaviour upon selecting multiple months:

Changes This is a simple change that adds the missing selected class (react-datepicker__month-text--selected) to the scenario of having selectsMultiple & showMonthYearPicker flags enabled

Screenshots

To reviewers

Contribution checklist

• [x] I have followed the contributing guidelines.
• [x] I have added sufficient test coverage for my changes.
• [x] I have formatted my code with Prettier and checked for linting issues with ESLint for code readability.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 96.67%. Comparing base (49299d5) to head (d82aa0c).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #4944 +/- ## ========================================== + Coverage 96.66% 96.67% +0.01% ========================================== Files 28 28 Lines 3264 3275 +11 Branches 1355 1357 +2 ========================================== + Hits 3155 3166 +11 Misses 109 109 ```

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[martijnrusschen]

This PR is lacking test coverage. Can you add that to ensure this won't break in the future?

[luistorres]

This PR is lacking test coverage. Can you add that to ensure this won't break in the future?

Yes, on it 👍

[luistorres]

@martijnrusschen should be fine now 😃

[martijnrusschen]

Perfect!