Do not trigger slideChange on the initial render.

[sparhami]

• Change the carousel implementation to stop notifying when the internal index did not actually change. Note that the initial change is from NaN to an actual index, so that will still notify.
• Change the carousel 0.2 code to only fire the slideChange event/action after the first one (from the initial render).

Closes #24706
Fixes #24701

[wassgha]

A bit confused as to why triggering the event on the initial render is what's causing the error in the issue. Could you clarify that?

[wassgha]

It's not possible to use the check that currentIndex_ is null instead of adding an instance variable here?

[sparhami]

Good call, made the change and also fixed #24701 in the process.

[sparhami]

A bit confused as to why triggering the event on the initial render is what's causing the error in the issue. Could you clarify that?

The problem is that on initial render, we trigger the slideChange with low trust (since the user did not interact) and we do not want it to be used for setState and such, since that could cause the page to jump.

As a result, the code that runs the action complains that you are trying to do a high trust required action with a low trust source.

[rcebulko]

@wassgha @sparhami I noticed this PR was submitted without owners approval. Should the OWNERS.yaml file in amp-carousel be updated/altered, and should an OWNERS.yaml file be added to amp-base-carousel?

For reference, see the current owners tree

[sparhami]

@wassgha @sparhami I noticed this PR was submitted without owners approval. Should the OWNERS.yaml file in amp-carousel be updated/altered, and should an OWNERS.yaml file be added to amp-base-carousel?

For reference, see the current owners tree

I created #24739 to update the relevant owners.