fix(item-sliding): restore side switching

[minwookshin]

Issue number: resolves #29975

What is the current behavior?

Opening the opposite side of an already-open item cancels the close timer but leaves item-sliding-closing and a disabled swipe gesture behind. The newly opened options cannot be clicked, and the item cannot be swiped closed.

What is the new behavior?

Cancelling that timer also removes the closing class and restores the gesture according to disabled. Normal closing and closing another open item keep their existing behavior.

Does this introduce a breaking change?

• Yes
• No

Other information

Added a manual reproduction at core/src/components/item-sliding/test/open/index.html and functional coverage for both switching directions, option clicks, swiping, disabled gestures, repeated switches, normal closing, and a second sliding item.

Validation: 54 tests passed across Chromium, Firefox, and WebKit in iOS and MD modes; the click and swipe regressions both fail against the unchanged base. Core unit tests passed (87 suites, 803 tests), as did the existing functional sliding tests (8 passed, 1 existing WebKit skip), the core build, scoped ESLint, and formatting checks. These are functional tests, so no screenshot baselines changed.

Programmatic open() in RTL still has the separate issue tracked as FW-3711 in the existing test helper. This PR follows that existing LTR restriction and does not claim to fix RTL.

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