…s and next months (#30262)

Issue number: Internal


## What is the new behavior?
<!-- Please describe the behavior or changes that are being added by
this PR. -->
Adds a new property to datetime, showAdjacentDays, that when true will
show the last days of the previous month and the first days of the next
month. This will just occupy empty "cells" at the beginning of the month
"table" and add rows to the table until a maximum of 6 rows are
displayed.

## Changes
- add styles for adjacent day button
- add `showAdjacentDays` property to datetime component
- change month generation to respect new property
- add visual tests to new feature

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

## Other information


[Preview](https://ionic-framework-git-rou-11118v2-ionic1.vercel.app/src/components/datetime/test/show-adjacent-days)

---------

Co-authored-by: Brandy Smith <brandyscarney@users.noreply.github.com>
Co-authored-by: Brandy Smith <6577830+brandyscarney@users.noreply.github.com>
Co-authored-by: Maria Hutt <thetaPC@users.noreply.github.com>

Issue number: internal

---------

<!-- Please do not submit updates to dependencies unless it fixes an
issue. -->

<!-- Please try to limit your pull request to one type (bugfix, feature,
etc). Submit multiple pull requests if needed. -->


## What is the new behavior?
<!-- Please describe the behavior or changes that are being added by
this PR. -->
Now when an adjacent day is selected the component will scroll to the
pretended month, as it does when a month change via arrow buttons.

## Changes:
- add styles for active adjacent day;
- scroll animation when adjacentDay is selected;

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

<!--
  If this introduces a breaking change:
1. Describe the impact and migration path for existing applications
below.
  2. Update the BREAKING.md file with the breaking change.
3. Add "BREAKING CHANGE: [...]" to the commit description when merging.
See
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for more information.
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## Other information

- [md
preview](https://ionic-framework-git-rou-11744-ionic1.vercel.app/src/components/datetime/test/show-adjacent-days?ionic:mode=md)
- [ios
preview](https://ionic-framework-git-rou-11744-ionic1.vercel.app/src/components/datetime/test/show-adjacent-days?ionic:mode=ios
)
<!-- Any other information that is important to this PR such as
screenshots of how the component looks before and after the change. -->

---------

Co-authored-by: Maria Hutt <thetaPC@users.noreply.github.com>
Co-authored-by: ionitron <hi@ionicframework.com>

…6-with-main