Track Media References in Custom Layout Builder Blocks [#3630805]

Problem/Motivation

Entity Usage does not track Media entities selected through Entity Browser widgets in custom Layout Builder block configuration fields.

This creates two gaps:

Usage Tracking: Media referenced in custom Layout Builder blocks does not appear in Entity Usage reports.
Unused Media Detection: Since these references are not tracked, media assets may be incorrectly identified as unused and accidentally removed.

Steps to reproduce

Create a custom Layout Builder block plugin.
Add a configuration field that allows selecting a Media entity through Entity Browser.
Place the custom block on a Layout Builder page.
Configure the block and select a media asset.
Save the page.
Open the selected Media entity and navigate to its Usage page.
Observe that the Layout Builder page is not listed as a usage.
Verify that no corresponding usage record is created by Entity Usage.

Proposed resolution

Requirement 1 Add support for tracking Media entity references stored in custom Layout Builder block configuration, including values populated through Entity Browser widgets.

Requirement 2: Provide code logic, an API, or a documented example to identify truly unused media entities, including validation against references stored in custom Layout Builder block configuration, so that unused media can be safely removed.