Create an interface for InlineBlockUsage

Patch looks good to me, making it public is also nice for contrib if they need to extend it (i.e. thinking of asymmetric translation if we decide it should not be part of core).

Change record written: https://www.drupal.org/node/3043944.

The interface docs look pretty basic, but it doesn't need to be elaborate at this point, since the inline block stuff isn't really an API. We can beef up the docs later as needed! +1 RTBC.

Yeah there's a couple small oddities in the docs, e.g.:

+++ b/core/modules/layout_builder/src/InlineBlockUsageInterface.php
@@ -0,0 +1,60 @@
+   * Delete the inline blocks' the usage records.

Extra "the".

However, since this is essentially moved code, fixing up the docs is out of scope.

That said:

FILE: .../layout_builder/src/EventSubscriber/SetInlineBlockDependency.php
----------------------------------------------------------------------
FOUND 0 ERRORS AND 1 WARNING AFFECTING 1 LINE
----------------------------------------------------------------------
 11 | WARNING | [x] Unused use statement
----------------------------------------------------------------------
PHPCBF CAN FIX THE 1 MARKED SNIFF VIOLATIONS AUTOMATICALLY
----------------------------------------------------------------------

Fixed on commit like so:

diff --git a/core/modules/layout_builder/src/EventSubscriber/SetInlineBlockDependency.php b/core/modules/layout_builder/src/EventSubscriber/SetInlineBlockDependency.php
index 7755e33d5c..23e965be86 100644
--- a/core/modules/layout_builder/src/EventSubscriber/SetInlineBlockDependency.php
+++ b/core/modules/layout_builder/src/EventSubscriber/SetInlineBlockDependency.php
@@ -8,7 +8,6 @@
 use Drupal\Core\Database\Connection;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\EntityTypeManagerInterface;
-use Drupal\layout_builder\InlineBlockUsage;
 use Drupal\layout_builder\InlineBlockUsageInterface;
 use Drupal\layout_builder\LayoutEntityHelperTrait;
 use Drupal\layout_builder\SectionStorage\SectionStorageManagerInterface;

Committed to 8.8.x, cherry-picked to 8.7.x, and published the change record. Thanks!