chore: remove any and resolve lint (#28782)

Issue number: Internal

---------

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## What is the current behavior?
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As part of FW-2832 the team has an initiative to remove much of the
`any` usage in favor of stronger types. This will make modifications to
this codebase safer as we will have access to proper type checking.

## What is the new behavior?
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this PR. -->

- Added stronger types to the `animationTimeout` variable. Making this
change causes our linter to fail because we are using a number value in
a conditional which we do not allow. To avoid this, I needed to check if
`animationTimeout` was `undefined`. This should not cause any changes
for Ionic developers, but I want to ship this a) in a separate patch and
b) in a minor release to de-risk just in case there's an edge case I am
not considering.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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## Other information

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screenshots of how the component looks before and after the change. -->

core/src/utils/helpers.ts

@@ -22,7 +22,7 @@ export const transitionEndAsync = (el: HTMLElement | null, expectedDuration = 0)
  */
 const transitionEnd = (el: HTMLElement | null, expectedDuration = 0, callback: (ev?: TransitionEvent) => void) => {
   let unRegTrans: (() => void) | undefined;
-  let animationTimeout: any;
+  let animationTimeout: number | undefined;
   const opts: any = { passive: true };
   const ANIMATION_FALLBACK_TIMEOUT = 500;
 
@@ -45,7 +45,7 @@ const transitionEnd = (el: HTMLElement | null, expectedDuration = 0, callback: (
     animationTimeout = setTimeout(onTransitionEnd, expectedDuration + ANIMATION_FALLBACK_TIMEOUT);
 
     unRegTrans = () => {
-      if (animationTimeout) {
+      if (animationTimeout !== undefined) {
         clearTimeout(animationTimeout);
         animationTimeout = undefined;
       }