4 string references to file.upload_handler

CKEditor5ImageController::create in core/modules/ckeditor5/src/Controller/CKEditor5ImageController.php
FileUploadHandlerTest::setUp in core/modules/file/tests/src/Kernel/FileUploadHandlerTest.php
FileUploadResource::create in core/modules/file/src/Plugin/rest/resource/FileUploadResource.php
LegacyFileUploadHandlerTest::testThrow in core/modules/file/tests/src/Kernel/Upload/LegacyFileUploadHandlerTest.php
@covers ::handleFileUpload

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