Consider a scenario where the background color and indicator's background color are the same. 

Adding a stroke color to the value indicator would be a valuable for the following reasons:
- **Visual Clarity:** It would allow developers to make the value indicator stand out more against the background, making it easier for users to notice.
- **Customization:** It would provide more flexibility in customizing the appearance of the sliding widget, allowing developers to match the design requirements of their apps.
- **Accessibility:** Improved visual distinction can enhance the accessibility of the sliding widget for users with various needs.

*List which issues are fixed by this PR. You must list at least one issue.*

Fixes #135984

## Description

This removes all of the comments that are of the form "so-and-so (must not be null|can ?not be null|must be non-null)" from the cases where those values are defines as non-nullable values.

This PR removes them from the material library.

This was done by hand, since it really didn't lend itself to scripting, so it needs to be more than just spot-checked, I think. I was careful to leave any comment that referred to parameters that were nullable, but I may have missed some.

In addition to being no longer relevant after null safety has been made the default, these comments were largely fragile, in that it was easy for them to get out of date, and not be accurate anymore anyhow.

This did create a number of constructor comments which basically say "Creates a [Foo].", but I don't really know how to avoid that in a large scale change, since there's not much you can really say in a lot of cases.  I think we might consider some leniency for constructors to the "Comment must be meaningful" style guidance (which we de facto have already, since there are a bunch of these).

## Related PRs
- https://github.com/flutter/flutter/pull/134984
- https://github.com/flutter/flutter/pull/134992
- https://github.com/flutter/flutter/pull/134993
- https://github.com/flutter/flutter/pull/134994

## Tests
 - Documentation only change.

design doc: https://docs.flutter.dev/go/permissible-slider-interaction

closes #113370

open questions:
  - No, as `SliderInteraction.none` doesn't exist anymore.
  - Yes (done)
  - Yes.
    - SliderInteraction
    - SliderAction
    - Slider.allowedInteraction
    - Slider.permissibleInteraction
    - Slider.interaction
    - Slider.allowedAction
    - Slider.permittedAction

Remove 1745 decorative breaks

* dart fix --apply

* manual fixes

* Add Material 3 support for Slider - Part 2

* Kick tests

* Update drawing order to fix html renderer bug

* Update test

* Use `curly_braces_in_flow_control_structures` for `material`

* include test/material

* add back removed comments

* migrates lib/foundation and lib/widgets

* migrates lib/painting and lib/material

* migrates lib/cupertino, lib/gestures, lib/services, lib/semantics and lib/rendering

* fixes failing tests

* migrates test/

* improves hashing of lists

Use additionalActiveTrackHeight when painting the radius of RoundedRectSliderTrackShape's active track (#85697)

Update samples to use repo analysis options, Fix sample templates and a ton of analyzer issues (#77868)

* migrate material to nullsafety

* address review comments

* address review comments

* fix build