IconButton, Tooltip: reduce per-instance cost of the built-in tooltip #8719

Part of #8676 (P1). Measure with #8714 before and after. This was blocked on #8562, which has merged.

Problem

Button/IconButton.tsx:60 wraps every labelled IconButton in a TooltipV2 unless unsafeDisableTooltip is set. Each tooltip instance:

• Registers a global Escape handler through useOnEscapePress (TooltipV2/Tooltip.tsx:289), even while the tooltip is closed.
• Runs an accessibility DOM scan on mount in production (:237-288). warning and invariant are no-ops in production, but their arguments are still computed.

hooks/useOnEscapePress.ts:75 and :82 also call Object.keys(registry) on every register and unregister.

Measured: median of 5 runs, N IconButtons:

Unmount cost grows super-linearly, about 58x for 10x the buttons. Mount cost grows slightly faster than linear. At a few hundred buttons the cost is small.

Proposed fix

• Subscribe to Escape only while the tooltip is open.
• Wrap the accessibility scan in __DEV__.
• Replace Object.keys(registry).length with a counter.

Don't lazy-mount the tooltip element, because aria-labelledby needs it in the DOM. The fix must work on React 18 and 19.

Acceptance criteria

• A closed tooltip doesn't register an Escape handler.
• The accessibility scan doesn't run in production builds.
• Escape still closes an open tooltip, and the existing Escape ordering tests still pass.
• aria-labelledby and aria-describedby wiring doesn't change.
• The PR reports before and after numbers from Add repeatable performance benchmarks for list, tree and button stress cases #8714.