bug: popover size is not working properly with an event (no trigger)

[brandyscarney]

Bug Report

Ionic version:

[ ] 4.x
[ ] 5.x
[x] 6.x

Current behavior:

Passing size: 'cover' when opening a popover using a popoverController is not working with an event without a trigger, the trigger is null

Expected behavior:

The popover should be using the element from the passed in event here:
https://github.com/ionic-team/ionic-framework/blob/next/core/src/components/popover/animations/ios.enter.ts#L22
https://github.com/ionic-team/ionic-framework/blob/next/core/src/components/popover/animations/md.enter.ts#L21

Steps to reproduce:

Can be reproduced on the next branch by passing size: cover with an event

[liamdebeasi]

Resolved via #23532.

[ionitron-bot]

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