This PR is to add **controller** property to the **Stepper** widget, so
that user has the flexibility to control the scroll offset for various
purposes(especially in case of scroll animations)!

Fixes #61207 
Co-authored-by: Taha Tesser <tessertaha@gmail.com>

[Stepper] adds stepIconBuilder property

Remove 1745 decorative breaks

* dart fix --apply

* manual fixes

* init

* upper case only when material 2

* fix test

* fix test

* fix tests again

* Add all tests

* analyze"

* fix stepper

* Add label on Step

* Add _buildLabelText, _labelStyle

* Update _buildHorizontal with _buildLabelText

* Fix Redundant Center widgets

* Fix Unnecessary Column Widget

* Fix Unnecessary import

* Fix Unnecessary Container

* Set label style to bodyText1 to match title style

* Update test for Alternative Label

* Fix code format

* Update label docstring

* Update to test textstyle of label

* Update to Test `TextStyles` of Label

* Fix typo in inline comments

* Update for Stepper type to `horizontal`

* Restore `_buildVerticalHeader`

* Update docstring, `Only [StepperType.horizontal]`

* Update for Readability

* Add `_isLabel` method

* Update `Horizontal height` with `_isLabel`

* Update to make `_buildIcon` centered

* Fix for `curly_braces_in_flow_control_structures`

* Use `curly_braces_in_flow_control_structures` for `material`

* include test/material

* add back removed comments

This does a cleanup of the examples, removing all of the "section" markers and extra comments that we don't need anymore now that the samples are no longer in the source code. It also removes the --template arguments from the {@tool dartpad} and {@tool sample} directives, since those are no longer used. It converts two examples that I discovered were still embedded into linked examples in the examples folder.

I didn't delete the templates from the snippets config folder yet, because there are still embedded samples in the dart:ui package from the engine that use them. Once dart:ui no longer uses the templates, they can be removed.

I bumped the version of the snippets package to pick up a change that allows removal of the --template argument.

* changed controlsBuilder signature

combined all parameters into ControlsDetails class

* sample fixes

* updates to docstrings

* switched to positional argument for stepper.controlsbuilder

* Merge branch 'master' into stepper-builder-fix

This extracts the sample code out from the API doc comments, and places them in separate files on disk, allowing running of the examples locally, testing them, and building of slightly larger examples.

* add marging to vertical stepper

* Remove tralling spaces

* Update docstring

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

* interactive dartpad sample added

* cleaner code

* removed extra spaces

* minor spaces added

* removed null returns

* migrate material to nullsafety

* address review comments

* address review comments

* fix build