Fix: Data Views: bulk deleting causes a countdown experience in modal

[Rishit30G]

What?

This PR is intended to fix: #64405

Why?

When bulk deleting items, the loading state numbers should not be changed in the modal

How?

initialItemCount is a ref that holds the initial number of items. The value of a ref persists across re-renders, so even if items.length changes, initialItemCount.current will still hold the original number of items.

Testing Instructions

Test on a site with at least 100+ pages. Here's a playground link that will spin up a version.
Open the Site Editor > Pages.
Switch to Grid layout.
Bulk edit and select all.
Move the items to trash.
Notice the modal counts down from 20.

Screenshots or screencast

Screen.Recording.2024-08-09.at.3.49.48.PM.mov

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Co-authored-by: Rishit30G <rishit30g@git.wordpress.org>
Co-authored-by: t-hamano <wildworks@git.wordpress.org>
Co-authored-by: annezazu <annezazu@git.wordpress.org>

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[Rishit30G]

Hey @t-hamano!
Would appreciate if you could please review this PR 🙇
For some reason, reviewer was not assigned to this PR

[t-hamano]

Thanks for the ping!

This approach seems reasonable to me, but I'm not familiar with bulk actions, so I'd like to add some reviewers who are familiar with this feature.

My other concern is that this issue will not only occur when deleting pages, but also when deleting patterns, templates, and template parts, i.e. here:

gutenberg/packages/editor/src/dataviews/actions/delete-post.tsx

Lines 63 to 64 in 02d0520

	'Delete %d item?',
	'Delete %d items?',

[Rishit30G]

No problem, thanks for assigning it to other reviewers! 🙇
Sure, if the other reviewers also agree upon this approach, I'll update the other pages as well 👍