Merge branch '3502060-form-api-validation' into '3.0.x'

Issue #3502060 - Add new plugin

See merge request !27

src/Plugin/FapiValidationFilter/UcfirstFilter.php

+<?php
+
+namespace Drupal\fapi_validation\Plugin\FapiValidationFilter;
+
+use Drupal\fapi_validation\FapiValidationFiltersInterface;
+
+/**
+ * Fapi Validation Plugin for Ucfirst filter.
+ *
+ * @FapiValidationFilter(
+ *   id = "ucfirst"
+ * )
+ */
+class UcfirstFilter implements FapiValidationFiltersInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function filter($value) {
+    return ucfirst($value);
+  }
+
+}