Fix advancementMode variables for time based advancements.

[gmajoulet]

Fix advancementMode variables for time based advancements. The advancement was set on Advancement.start() which is called when the page starts playing, rather than on Advancement.onAdvance().

Fixes #26579

[newmuis]

Sorry; why is it incorrect to set it when the page starts playing? It should still be set when the story-page-visible trigger gets sent, right?

But for all other triggers, the page is currently auto-advancing, and the analytics variables should reflect that.

[gmajoulet]

The name is confusing and could mean either what you said, or what this PR is doing.
We implemented this while working on the branching feature, to have a way to know how the user got to a specific page.

If we wanted to have an API to know if the current page has an auto-advance attribute we'd need to add a new one. This one is used to track which one of the 6 ways to navigate has been used to get to this page.

amphtml/extensions/amp-story/1.0/story-analytics.js

Lines 45 to 53 in be3317a

	/** @enum {string} */
	export const AdvancementMode = {
	GO_TO_PAGE: 'goToPageAction',
	AUTO_ADVANCE_TIME: 'autoAdvanceTime',
	AUTO_ADVANCE_MEDIA: 'autoAdvanceMedia',
	MANUAL_ADVANCE: 'manualAdvance',
	ADVANCE_TO_ADS: 'manualAdvanceFromAd',
	VIEWER_SELECT_PAGE: 'viewerSelectPage',
	};

Changing it would mean refactoring all the other instances where we set the advancementMode

[gmajoulet]

Friendly ping
Let's discuss this during standup this morning if more context is needed :))

[newmuis]

Whoops, thought I had already lifted my "request changes"

LGTM ✅