file_validate and related functions are deprecated

Problem/Motivation

Trying to use the Node import via file fails because the code still uses the deprecated file_validate function.
https://www.drupal.org/node/3363700

Steps to reproduce

Upload an exported JSON at /admin/content/import/file gets the following error:
Drupal\Component\Plugin\Exception\PluginNotFoundException: The "file_validate_extensions" plugin does not exist. Valid plugin IDs for Drupal\Core\Validation\ConstraintManager are: Callback, Blank, NotBlank, Email, Choice, File, Image, PositiveOrZero, IdenticalTo, BlockContentEntityChanged, CKEditor5Element, CKEditor5MediaAndFilterSettingsInSync, CKEditor5EnabledConfigurablePlugins, CKEditor5FundamentalCompatibility, SourceEditingPreventSelfXssConstraint, SourceEditingRedundantTags, StyleSensibleElement, CKEditor5ToolbarItemConditionsMet, CKEditor5ToolbarItem, CKEditor5ToolbarItemDependencyConstraint, UniqueLabelInList, CommentName, DateTimeFormat, FileEncoding, FileExtension, FileExtensionSecure, FileImageDimensions, FileIsImage, FileNameLength, FileSizeLimit, FileUriUnique, FileValidation, LinkAccess, LinkExternalProtocols, LinkNotExistingInternal, LinkType, MenuTreeHierarchy, MenuSettings, PathAlias, TaxonomyHierarchy, ProtectedUserField, RoleExists, UserCancelMethod, UserMailRequired, UserMailUnique, UserName, UserNameUnique, ConfigExists, LangcodeRequiredIfTranslatableValues, RequiredConfigDependencies, Bundle, EntityChanged, EntityHasField, EntityType, EntityUntranslatableFields, ImmutableProperties, ReferenceAccess, ValidReference, ExtensionAvailable, ExtensionExists, ExtensionName, MenuLinkDepth, UniquePathAlias, ValidPath, PluginExists, AllowedValues, AtLeastOneOf, ClassResolver, ComplexData, Count, CountryCode, EntityBundleExists, FullyValidatable, Null, Length, MappingCollection, NotNull, Optional, PrimitiveType, Range, Regex, Required, Sequentially, Serialized, UniqueField, UriHost, Uuid, ValidKeys, ValidSequenceKeys in Drupal\Core\Plugin\DefaultPluginManager->doGetDefinition() (line 53 of /home/wwwuniae/arco/core/lib/Drupal/Component/Plugin/Discovery/DiscoveryTrait.php).

Proposed resolution

Replace in /node_export/src/Form/NodeImportFile.php line 48 with
$validators = ['FileExtension' => ['extensions' => 'json']];