Fixes #140770 and #103124
Adds the possibility of passing a height and width to icons. And also a margin for the distance of the lines between the icons.
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.
