Fix the Collator return types in phpdoc

The types were incoherent with the PHP documentation. There are still
some issues with types (e.g. constructor should not accept `null`
value). But changing them would break the API so I thought it wasn't a
good idea to fix them.

Reference: https://www.php.net/manual/class.collator.php

Author: marien-probesys

src/Intl/Icu/Collator.php

@@ -120,7 +120,7 @@ public function asort(array &$array, int $flags = self::SORT_REGULAR)
     /**
      * Not supported. Compare two Unicode strings.
      *
-     * @return bool|int
+     * @return int|false
      *
      * @see https://php.net/collator.compare
      *
@@ -134,7 +134,7 @@ public function compare(string $string1, string $string2)
     /**
      * Not supported. Get a value of an integer collator attribute.
      *
-     * @return bool|int The attribute value on success or false on error
+     * @return int|false The attribute value on success or false on error
      *
      * @see https://php.net/collator.getattribute
      *
@@ -148,7 +148,7 @@ public function getAttribute(int $attribute)
     /**
      * Returns collator's last error code. Always returns the U_ZERO_ERROR class constant value.
      *
-     * @return int The error code from last collator call
+     * @return int|false The error code from last collator call
      */
     public function getErrorCode()
     {
@@ -158,7 +158,7 @@ public function getErrorCode()
     /**
      * Returns collator's last error message. Always returns the U_ZERO_ERROR_MESSAGE class constant value.
      *
-     * @return string The error message from last collator call
+     * @return string|false The error message from last collator call
      */
     public function getErrorMessage()
     {
@@ -168,8 +168,8 @@ public function getErrorMessage()
     /**
      * Returns the collator's locale.
      *
-     * @return string The locale used to create the collator. Currently always
-     *                returns "en".
+     * @return string|false The locale used to create the collator. Currently
+     *                      always returns "en".
      */
     public function getLocale(int $type = Locale::ACTUAL_LOCALE)
     {
@@ -179,7 +179,7 @@ public function getLocale(int $type = Locale::ACTUAL_LOCALE)
     /**
      * Not supported. Get sorting key for a string.
      *
-     * @return string The collation key for $string
+     * @return string|false The collation key for $string
      *
      * @see https://php.net/collator.getsortkey
      *
@@ -193,7 +193,7 @@ public function getSortKey(string $string)
     /**
      * Not supported. Get current collator's strength.
      *
-     * @return bool|int The current collator's strength or false on failure
+     * @return int The current collator's strength or false on failure
      *
      * @see https://php.net/collator.getstrength
      *