feature #31295 [Intl] Add timezone offset utilities (ro0NL)

This PR was merged into the 4.3-dev branch.

Discussion
----------

[Intl] Add timezone offset utilities

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no
| Tests pass?   | yes (including intl-data group)
| Fixed tickets | #...   <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | symfony/symfony-docs#... <!-- required for new features -->

Commits
-------

b166e33 [Intl] Add timezone offset utilities

src/Symfony/Component/Intl/Tests/TimezonesTest.php

@@ -529,4 +529,18 @@ public function testExists()
         $this->assertTrue(Timezones::exists('Europe/Amsterdam'));
         $this->assertFalse(Timezones::exists('Etc/Unknown'));
     }
+
+    public function testGetRawOffset()
+    {
+        $this->assertSame(0, Timezones::getRawOffset('Etc/UTC'));
+        $this->assertSame(-10800, Timezones::getRawOffset('America/Buenos_Aires'));
+        $this->assertSame(20700, Timezones::getRawOffset('Asia/Katmandu'));
+    }
+
+    public function testGetGmtOffset()
+    {
+        $this->assertSame('GMT+00:00', Timezones::getGmtOffset('Etc/UTC'));
+        $this->assertSame('GMT-03:00', Timezones::getGmtOffset('America/Buenos_Aires'));
+        $this->assertSame('GMT+05:45', Timezones::getGmtOffset('Asia/Katmandu'));
+    }
 }

src/Symfony/Component/Intl/Timezones.php

@@ -12,6 +12,7 @@
 namespace Symfony\Component\Intl;
 
 use Symfony\Component\Intl\Exception\MissingResourceException;
+use Symfony\Component\Intl\Exception\RuntimeException;
 
 /**
  * Gives access to timezone-related ICU data.
@@ -52,6 +53,29 @@ public static function getNames(string $displayLocale = null): array
         return self::asort(self::readEntry(['Names'], $displayLocale), $displayLocale);
     }
 
+    public static function getRawOffset(string $timezone, int $timestamp = null): int
+    {
+        if (null === $timestamp) {
+            $timestamp = time();
+        }
+
+        $transitions = (new \DateTimeZone($timezone))->getTransitions($timestamp, $timestamp);
+
+        if (!isset($transitions[0]['offset'])) {
+            throw new RuntimeException('No timezone transitions available.');
+        }
+
+        return $transitions[0]['offset'];
+    }
+
+    public static function getGmtOffset(string $timezone, int $timestamp = null): string
+    {
+        $offset = self::getRawOffset($timezone, $timestamp);
+        $abs = abs($offset);
+
+        return sprintf('GMT%s%02d:%02d', 0 <= $offset ? '+' : '-', $abs / 3600, $abs / 60 % 60);
+    }
+
     protected static function getPath(): string
     {
         return Intl::getDataDirectory().'/'.Intl::TIMEZONE_DIR;