add: batch delete action for media grid

[JDeepD]

Fixes: #54016

Current implementation of bulk attachment deletion in media (grid view) initiates an AJAX request per attachment. This patch implements a new AJAX action for bulk post deletion and rewrites the logic for bulk deletion in frontend.

Trac ticket: https://core.trac.wordpress.org/ticket/54016

Use of AI Tools

AI assistance: Yes
Tool(s): GitHub Copilot, Claude
Model(s): Opus 4.6
Used for: Researching on batch processing, finding out edge cases in implementation and code suggestions.

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[github-actions]

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[JDeepD]

Currently, in the draft patch, I am seeing significant performance improvements when delete actions are batched. Here are the profiling results comparing trunk to this patch:

Action: Deleting 100 attachments in bulk from Media in 3G throttling

I will have to test it a bit more to make sure there are no edge cases with different file types and file sizes.

[JDeepD]

Current implementation:

bulk-delete-1.mp4

Batched actions

bulk-delete-2.mp4

[github-actions]

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