Fix TypeError when a component is disposed mid-transition

[MizouziE]

Description

Skip a component's queued transition-completion callback if the instance was disposed before the transition finished.

dispose() nulls every property on the instance but cannot cancel a callback already queued via executeAfterTransition as that helper registers a transitionend listener plus a setTimeout fallback, and neither can be cancelled. The callback then runs against a gutted instance and throws.

This deliberately does not null-guard Tooltip._isWithActiveTrigger(), the fix proposed in #37474. As noted there, that is only a defensive patch, and it just relocates the crash two lines down to this._element.removeAttribute('aria-describedby'). Better the queued callback not run at all.

Since every component routes transition completion through BaseComponent._queueCallback, guarding that single method fixes it for all of them at once. _element is already nulled by dispose(), so it doubles as the disposed flag and no new state, and executeAfterTransition's signature is untouched. Nothing leaks by skipping the callback: Modal and Offcanvas already dispose their backdrop and focustrap explicitly in their own dispose().

Motivation & Context

Fixes the long-standing Uncaught TypeError: Cannot convert undefined or null to object from Tooltip._isWithActiveTrigger() when a component is disposed mid-transition. Reported repeatedly since 2022 and typically worked around with a setTimeout before dispose().

dispose() is public API with no documented restriction against calling it during a transition, and the common trigger is not misuse: a MutationObserver disposing a tooltip whose trigger element was just removed from the DOM has no way to know a fade is still in flight.

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would change existing functionality)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

Live previews

• https://deploy-preview-42858--twbs-bootstrap.netlify.app/

Related issues

Closes #37474 (if reopened, I have added a comment/request there)
Related: #39743