7 files declare their use of FormHelper

common.inc in core/includes/common.inc
Common functions that many Drupal modules will need to reference.
EntityField.php in core/modules/views/src/Plugin/views/field/EntityField.php
FieldBlock.php in core/modules/layout_builder/src/Plugin/Block/FieldBlock.php
FilterPluginBase.php in core/modules/views/src/Plugin/views/filter/FilterPluginBase.php
FormHelperTest.php in core/tests/Drupal/Tests/Core/Form/FormHelperTest.php
Renderer.php in core/lib/Drupal/Core/Render/Renderer.php
RendererLegacyTest.php in core/tests/Drupal/KernelTests/Core/Render/RendererLegacyTest.php

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