dev: use WP_Filesystem for Signature Field uploads

CHANGELOG.md

@@ -14,6 +14,7 @@
 - feat: Add support for WPGraphQL Content Blocks.
 - dev: Remove `vendor` directory from the GitHub repository.
 - dev: Use `FormFieldsDataLoader` to resolve fields instead of instantiating a new `Model`.
+- dev: use WP_Filesystem to handle Signature field uploads.
 - chore!: Remove deprecated fields from the schema: `FormsConnectionOrderbyInput.field`, `GfFieldWithDisableQuantitySetting.isQuantityDisabled`. `GfSubmittedEntry.entryId`. `GfForm.button`, `gfForm.entryId`, `gfForm.lastPageButton`.
 - chore!: Remove deprecated hooks: `graphql_gf_form_modeled_data_experimental`, `graphql_gf_form_field_setting_properties`, `graphql_gf_form_field_value_properties`.
 - chore!: Remove deprecated helper method: `GFUtils::handle_file_upload()`.

src/Extensions/GFSignature/Data/FieldValueInput/SignatureValuesInput.php

@@ -88,8 +88,16 @@ protected function save_signature( string $signature ): string {
 		$folder   = \GFSignature::get_signatures_folder();
 		$filename = uniqid( '', true ) . '.png';
 		$path     = $folder . $filename;
-		// @todo: switch to WP Filesystem.
-		$number_of_bytes = file_put_contents( $path, $signature_decoded ); //phpcs:ignore WordPress.WP.AlternativeFunctions.file_system_read_file_put_contents, WordPressVIPMinimum.Functions.RestrictedFunctions.file_ops_file_put_contents
+
+		// Use WP_Filesystem to save the signature image.
+		global $wp_filesystem;
+		if ( ! $wp_filesystem instanceof \WP_Filesystem_Base ) {
+			require_once ABSPATH . 'wp-admin/includes/file.php';
+			WP_Filesystem();
+		}
+
+		/** @var \WP_Filesystem_Base $wp_filesystem */
+		$number_of_bytes = $wp_filesystem->put_contents( $path, $signature_decoded, FS_CHMOD_FILE );
 
 		if ( false === $number_of_bytes ) {
 			throw new UserError( esc_html__( 'An error occurred while saving the signature image.', 'wp-graphql-gravity-forms' ) );