Re-add nested portals

[r100-stack]

Changes

Reverts #2209 as the fix for #2205 (comment). Did this revert after internal discussion after we realized that a simpler alternative fix also works.

The simpler alternative to #2209 is to move focus to the DatePicker's today's date (second popover) only after it has been portaled to be a descendant of DateRangeFilter. Since floating-ui's FloatingFocusManager uses DOM events instead of React events (floating-ui/floating-ui#3060), waiting for the second popover to be portaled within the first is important to prevent a focus out being triggered on the first popover.

Additionally, I was unable to figure out how #2209 fixed the bug. Because after #2209, the second popover was moved outside the DOM of the first popover. So, focusing the second popover should be treated as a focus out of the first popover prompting the first popover to close. But it didn't. Since we're unable to figure out why it happens, reverting is safer as it brings a more reliable and predictable state.

Testing

• Fix failing unit tests
• Approved failing Table test images. Some of them may be reverts of the test images approved in #2209.
  • Even though the new images show that focus does not move to the correct element in the floating content (even with cy.wait()), I manually confirmed that focus moves correctly to the expected element in the floating content.
  • Additionally, the images with the incorrect focus were approved before #2209. So, it's okay to re-approve these images that don't have the focus on the correct element?

Docs

Not sure if a changeset is needed since I don't think it's a significant user facing change.

After PR TODO:

• Could consider a general "overridable initial focus" mechanism. Would be useful in Dialog too. (#2297)

[mayank99]

This needs a changeset because it has a pretty noticeable impact for users. And doesn't it also fix #2245?

[r100-stack]

This needs a changeset because it has a pretty noticeable impact for users.

Added the changeset nearly identical to the one from #2209. Can make it more specific if needed. Didn't think it was needed since the exact details of the fix in #2209 weren't added in its changeset.

And doesn't it also fix #2245?

Yes, it fixes #2245 and #2291. I tested it by confirming that the nested popovers in the playgrounds' code no longer close unexpectedly.

Screen-recordings

PR	Before	After
#2245	before.mov	after.mov
#2291	before.mov	after.mov

[smmr-dn]

LGTM!

[jason-crow]

@mayank99 when can we expect this PR to merge in and a patch published including it? This is needed to resolve a blocker for our pending release and it seems like the PR is approved, so I'm hoping this can complete and publish today?

[r100-stack]

when can we expect this PR to merge in and a patch published including it?

This patch fix has now been released in 3.15.4 🚀