feat(ui5-slider): support custom values via tickmarks property

[MapTo0]

Summary

• Adds a public tickmarks property to ui5-slider enabling custom non-numeric labels on tick marks
• When tickmarks is set, the slider snaps only to defined values, displays custom labels, and announces them via aria-valuetext
• Auto-derives min/max from tickmark values and auto-shows tickmarks — zero boilerplate for consumers

API

slider.tickmarks = [
  { value: 0, label: "Freezing" },
  { value: 25, label: "Room Temp" },
  { value: 50, label: "Warm" },
  { value: 100, label: "Boiling" }
];

Behavior in custom values mode

• Handle snaps to nearest defined tickmark value on click/drag
• Arrow keys navigate to next/previous tickmark value
• Home/End jump to first/last value
• Ctrl+Arrow/PageUp/PageDown jump by ~1/10th of tickmark count
• Tooltip displays custom label
• Editable tooltip is disabled (only defined values are valid)
• aria-valuetext set for screen reader accessibility
• step, min, max, showTickmarks are ignored when tickmarks is provided

Scope

This is the POC implementation for Slider only. Range Slider support will follow in Phase 2 after it is refactored to use SliderScale.

Resolves #9730, resolves #9058
Related: BGSOFUIRILA-4125

Test plan

• 11 new Cypress tests covering: rendering, click snapping, keyboard navigation, Home/End, handle positioning, aria-valuetext, tooltip label, auto-derived min/max, auto-show tickmarks, backward compatibility
• All 55 existing + new Slider tests pass
• TypeScript compiles cleanly
• Manual testing via test page at /test/pages/Slider.html (Custom Values section)

[ui5-webcomponents-bot]

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