Fix peer resize handles appearing during resize

[dvd233]

Description

Fixes #3226.

Track the active resize separately from the resizable currently under the pointer. While a resize is active, peer hover state is recorded without revealing its handles. Normal hover visibility is restored when the resize ends.

The active resize state is internal, so this does not expand the public TypeScript declarations.

Verification

• yarn test — 383 core tests and 6 React tests passed
• yarn build — core, Angular, React, Vue, and generated docs built successfully
• Chromium browser check — peer handle stayed display: none during resize and returned to display: block on mouseup

Checklist

• Created tests which fail without the change (if possible)
• All tests passing (yarn test)
• Extended the README / documentation, if necessary