A11Y : fix issues due to 4.1.0 (Multiple Select2)

[f2cmb]

• I have read the CONTRIBUTING document.
• I have performed a self-review of my code.
• I have added tests that prove my fix is effective or that my feature works.

Description

• one fixe for Fix dropdowns accessibility roadmap#310 that comes from : build(deps): bump select2 from 4.0.13 to 4.1.0 #24438, as 4.1.0 ships an improvment for a11y (close button is now a real button)

• Here is a brief description of what this PR does :

Finishes the 4.1.0 bump from #24438. Kept because the chip's remove control is now a real <button aria-label="Remove item"> (keyboard/screen-reader reachable) instead of a decorative <span>. The raw bump broke our overrides, so I adapted the SCSS to the new chip layout: padding-left to stop the × overlapping the text, margin-left restored so the first chip isn't glued to the left edge, styled the search field (now a <textarea>), and renamed the removed containerCssClass option to selectionCssClass.

It's one global rule, no per-screen special-casing. Checked live on Forms, ITIL, Assets and Config: renders as before, minus the overlap. New dropdown_a11y.spec.ts locks the accessible button (fails on 4.0.13, passes on 4.1.0).

Screenshots :