Add soft scale animations to Tooltip and Popover

[iu-glints]

What changed

• replace the 400ms Tooltip fade with a 240ms soft-scale entrance and 120ms exit
• add the same 240ms soft-scale entrance to Popover, with a 90ms exit that completes before Polaris unmounts the overlay
• preserve placement transforms by animating the independent CSS scale property
• disable motion when prefers-reduced-motion is enabled
• cover both components’ animation timings and scale endpoints with style tests

Verification

• yarn test --runInBand src/@next/Popover/PopoverStyle.test.tsx src/@next/Tooltip/TooltipStyle.test.tsx
• yarn lint:css
• pre-commit TypeScript lint and Prettier checks
• yarn build:ts