40 files declare their use of Inspector

ApcuBackend.php in core/lib/Drupal/Core/Cache/ApcuBackend.php
Cache.php in core/lib/Drupal/Core/Cache/Cache.php
CacheableNormalization.php in core/modules/jsonapi/src/Normalizer/Value/CacheableNormalization.php
CacheCollector.php in core/lib/Drupal/Core/Cache/CacheCollector.php
CacheTagsInvalidator.php in core/lib/Drupal/Core/Cache/CacheTagsInvalidator.php
CKEditor4To5UpgradePluginManager.php in core/modules/ckeditor5/src/Plugin/CKEditor4To5UpgradePluginManager.php
CKEditor5PluginDefinition.php in core/modules/ckeditor5/src/Plugin/CKEditor5PluginDefinition.php
CKEditor5PluginManager.php in core/modules/ckeditor5/src/Plugin/CKEditor5PluginManager.php
ComponentPluginManager.php in core/modules/sdc/src/ComponentPluginManager.php
ComponentPluginManager.php in core/lib/Drupal/Core/Theme/ComponentPluginManager.php
Connection.php in core/lib/Drupal/Core/Database/Connection.php
Data.php in core/modules/jsonapi/src/JsonApiResource/Data.php
DatabaseBackend.php in core/lib/Drupal/Core/Cache/DatabaseBackend.php
DefaultPluginManager.php in core/lib/Drupal/Core/Plugin/DefaultPluginManager.php
EntityResource.php in core/modules/jsonapi/src/Controller/EntityResource.php
EntityResourceTestBase.php in core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
ErrorCollection.php in core/modules/jsonapi/src/JsonApiResource/ErrorCollection.php
HTMLRestrictions.php in core/modules/ckeditor5/src/HTMLRestrictions.php
IncludedData.php in core/modules/jsonapi/src/JsonApiResource/IncludedData.php
InspectorTest.php in core/tests/Drupal/Tests/Component/Assertion/InspectorTest.php
InstallConfigurator.php in core/lib/Drupal/Core/Recipe/InstallConfigurator.php
LayoutBuilderController.php in core/modules/layout_builder/src/Controller/LayoutBuilderController.php
Link.php in core/modules/jsonapi/src/JsonApiResource/Link.php
LinkCollection.php in core/modules/jsonapi/src/JsonApiResource/LinkCollection.php
MemoryBackend.php in core/lib/Drupal/Core/Cache/MemoryBackend.php
MemoryCache.php in core/lib/Drupal/Core/Cache/MemoryCache/MemoryCache.php
OmittedData.php in core/modules/jsonapi/src/JsonApiResource/OmittedData.php
PermissionsPerBundle.php in core/lib/Drupal/Core/Config/Action/Plugin/ConfigAction/PermissionsPerBundle.php
PhpBackend.php in core/lib/Drupal/Core/Cache/PhpBackend.php
PhpTufValidator.php in core/modules/package_manager/src/Validator/PhpTufValidator.php
RecipeMissingExtensionsException.php in core/lib/Drupal/Core/Recipe/RecipeMissingExtensionsException.php
RelationshipData.php in core/modules/jsonapi/src/JsonApiResource/RelationshipData.php
ResourceObjectData.php in core/modules/jsonapi/src/JsonApiResource/ResourceObjectData.php
ResourceTypeBuildEvent.php in core/modules/jsonapi/src/ResourceType/ResourceTypeBuildEvent.php
ResourceTypeRepository.php in core/modules/jsonapi/src/ResourceType/ResourceTypeRepository.php
SmartDefaultSettings.php in core/modules/ckeditor5/src/SmartDefaultSettings.php
StagedDBUpdateValidator.php in core/modules/package_manager/src/Validator/StagedDBUpdateValidator.php
user.module in core/modules/user/user.module
Enables the user registration and login system.
ValidationResult.php in core/modules/package_manager/src/ValidationResult.php
WorkspaceRepository.php in core/modules/workspaces/src/WorkspaceRepository.php

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