Share common markup for PHP 8.0 release page translations

Apart from the following exceptions, no content or translations have been changed.

Content and layout improvements:

* Added IDs to headings in section above footer for direct linking.
* Added `<code>` tag around operators and keywords for better readability.
* Moved Just-In-Time Compilation section to a half-width column rather than full-width. This is more consistent with the other release pages, and makes it easier to read the description on large screens since the paragraph isn't so excessively wide.
* Updated code examples to use 4-space indentation rather than 2-space, for consistency with all the other release pages.
* Updated the "New Classes, Interfaces, and Functions" section to show the actual class name for `WeakMap` and `PhpToken` (which removed the need for translation there).
* Moved both RFC links after the text for "Allow a trailing comma in parameter lists and closure use lists" for simplicity and consistency across translations.

Translation-specific fixes and changes:

* Fixed bug where header links in the French and Japanese translations unexpectedly switched to the English translation of the page (caused by incorrect `$_SERVER['BASE_PAGE']` value).
* French translation previously had a different code example for attributes, which didn't really make sense (it showed the same `/api/posts/{id}` Route attribute, but above a User class rather than on a `get` method in a PostsController class).
* Fixed incorrect Static Return Type RFC link in Portuguese translation.
* Fixed a couple minor spacing bugs in Spanish translation.
* Fixed missing blank lines in a few Chinese translation code blocks.
* Georgian translation previously changed strings/comments in the code examples for Union Types and Match Expression. If this is still wanted we could add translation strings to include in these code blocks, but I don't think it's worth it since the examples already have translated descriptions, and these code blocks weren't altered for any other languages.

Author: theodorejb

releases/8.0/common.php

@@ -69,3 +69,13 @@ function language_chooser(string $currentLang): void {
       </form>
 ';
 }
+
+function message($code, $language = 'en')
+{
+    $original = require __DIR__ . '/languages/en.php';
+    if (($language !== 'en') && file_exists(__DIR__ . '/languages/' . $language . '.php')) {
+        $translation = require __DIR__ . '/languages/' . $language . '.php';
+    }
+
+    return $translation[$code] ?? $original[$code] ?? $code;
+}