Translator: Add strict type declarations

This change requires adjustments to the following consumers:

ipl-i18n
    - src/GettextTranslator.php
    - src/NoopTranslator.php

PHPDoc adjusted: nullable shorthand, union type ordering, compact format.

Author: Jan-Schuppik

src/Contract/Translator.php

@@ -11,11 +11,11 @@ interface Translator
      * Translate a message
      *
      * @param string $message
-     * @param string $context Message context
+     * @param ?string $context Message context
      *
      * @return string Translated message or original message if no translation is found
      */
-    public function translate($message, $context = null);
+    public function translate(string $message, ?string $context = null): string;
 
     /**
      * Translate a message in the given domain
@@ -24,11 +24,11 @@ public function translate($message, $context = null);
      *
      * @param string $domain
      * @param string $message
-     * @param string $context Message context
+     * @param ?string $context Message context
      *
      * @return string Translated message or original message if no translation is found
      */
-    public function translateInDomain($domain, $message, $context = null);
+    public function translateInDomain(string $domain, string $message, ?string $context = null): string;
 
     /**
      * Translate a plural message
@@ -37,13 +37,13 @@ public function translateInDomain($domain, $message, $context = null);
      * That is also the case if no translation is found.
      *
      * @param string $singular Singular message
-     * @param string $plural   Plural message
-     * @param int    $number   Number to decide between the returned singular and plural forms
-     * @param string $context  Message context
+     * @param string $plural Plural message
+     * @param int $number Number to decide between the returned singular and plural forms
+     * @param ?string $context Message context
      *
      * @return string Translated message or original message if no translation is found
      */
-    public function translatePlural($singular, $plural, $number, $context = null);
+    public function translatePlural(string $singular, string $plural, int $number, ?string $context = null): string;
 
     /**
      * Translate a plural message in the given domain
@@ -55,11 +55,17 @@ public function translatePlural($singular, $plural, $number, $context = null);
      *
      * @param string $domain
      * @param string $singular Singular message
-     * @param string $plural   Plural message
-     * @param int    $number   Number to decide between the returned singular and plural forms
-     * @param string $context  Message context
+     * @param string $plural Plural message
+     * @param int $number Number to decide between the returned singular and plural forms
+     * @param ?string $context Message context
      *
      * @return string Translated message or original message if no translation is found
      */
-    public function translatePluralInDomain($domain, $singular, $plural, $number, $context = null);
+    public function translatePluralInDomain(
+        string $domain,
+        string $singular,
+        string $plural,
+        int $number,
+        ?string $context = null
+    ): string;
 }