API Use new RememberLoginHash::onAfterRenewSession extension point

[Cheddam]

Description

This extension point is triggered at the same step as the now-removed onAfterRenewToken extension point, which was replaced to reflect that the token is no longer rotated when a session renewal is triggered.

I've also added some comments to more clearly articulate the session identifier replacement logic - I considered pulling this out instead, but for efficiency it makes sense to retain.

Co-dependent on related framework PR: silverstripe/silverstripe-framework#11355

Manual testing steps

Checkout this PR along with the Framework PR and validate that remember me functionality is intact.

Issues

• Remember Me functionality fails when renewal is interrupted silverstripe-framework#11281

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