General: Add a test to check that unicode generally survives in slugs

Until now, WordPress generated all-ASCII slugs, which works well for
mostly-ASCII languages. Now that WordPress supports scripts like
Devanagari much better, it's necessary to test the slug support for
Devanagari. What WordPress did until now works well for Devanagari, so
this commit merely adds a unit test.

The ideal is to have links such as
	<hebrewdomain>.<hebrewtld>/<hebrewpath>
which is shown onscreen as
	<hebrewpath>/<hebrewtld>.<hebrewdomain>
without any switches between right-to-left Hebrew and left-to-right Latin.
/author/ and a few others don't achieve that ideal. Yet.

Note that there is a rare existing bug: The existing mapping to ASCII can
produce the same slug for two pages, since two letters can map to e.g.
'L'. This seems unfixable, since any change might break existing links,
but happily also extremely rare.

Author: arnt

tests/phpunit/tests/formatting/sanitizeTitle.php

@@ -12,6 +12,11 @@ public function test_strips_html() {
 		$this->assertSame( $expected, sanitize_title( $input ) );
 	}
 
+	public function test_leaves_devanagari() {
+		$input = 'राजीव';
+		$this->assertSame( $input, urldecode( sanitize_title( $input ) ) );
+	}
+
 	public function test_titles_sanitized_to_nothing_are_replaced_with_optional_fallback() {
 		$input    = '<strong></strong>';
 		$fallback = 'Captain Awesome';