Step rounding to use min as step base (element is not a valid number)

Problem/Motivation

The new implementation with the range-slider-element behaviour conflicts with step validation for range inputs. Instead of rounding steps relative to the min attribute (the step base), it does so relative to 0.
This causes range sliders to snap to incorrect values when min is not a multiple of step, violating the HTML5 specification and providing unexpected user experience.

Steps to reproduce

Create a slider using these attributes:

$form['slider'] = [
  '#type' => 'range_slider',
  '#min' => 5,
  '#max' => 30,
  '#step' => 2,
  '#default_value' => 6,
];

Results in:

Proposed resolution

See if the issue can be fixed upstream first https://github.com/andreruffert/range-slider-element/pull/210

Remaining tasks

User interface changes

API changes

Data model changes