feat(VSkeletonLoader): add chip-group and timeline-item skeleton types

[sridhar-3009]

Summary

Fixes #20695 and #20451 — adds chip-group, timeline-item, timeline-item-two, and timeline-item-three skeleton loader types.

New types

Type	Composition
chip-group	5 chips in a wrapping row
timeline-item	avatar marker + single-line heading
timeline-item-two	avatar marker + two-line sentences
timeline-item-three	avatar marker + three-line paragraph

Usage

<v-skeleton-loader type="chip-group" />
<v-skeleton-loader type="timeline-item" />
<v-skeleton-loader type="timeline-item-three@3" />

Test plan

• Render type="chip-group" — should show a wrapping row of chip-shaped skeletons
• Render type="timeline-item" — should show an avatar (marker) beside a heading
• Render type="timeline-item-two" — avatar + two-line text
• Render type="timeline-item-three@3" — stacked timeline items with avatar + paragraph