Fix backwards compatibility alias for WordAccumulator

This was a mistake in I892364b. Unfortunately the codebase was in a
confusing state with many classes in no namespace. But this class was
in one.

Bug: T339184
Change-Id: Id31b9f53ffb6483c1901db8ab26fcb40368ec074

autoload.php

@@ -1063,6 +1063,7 @@ $wgAutoloadLocalClasses = [
 	'MediaWiki\\Diff\\Hook\\DifferenceEngineViewHeaderHook' => __DIR__ . '/includes/diff/Hook/DifferenceEngineViewHeaderHook.php',
 	'MediaWiki\\Diff\\Hook\\NewDifferenceEngineHook' => __DIR__ . '/includes/diff/Hook/NewDifferenceEngineHook.php',
 	'MediaWiki\\Diff\\Hook\\TextSlotDiffRendererTablePrefixHook' => __DIR__ . '/includes/diff/Hook/TextSlotDiffRendererTablePrefixHook.php',
+	'MediaWiki\\Diff\\WordAccumulator' => __DIR__ . '/includes/libs/Diff/WordAccumulator.php',
 	'MediaWiki\\EditPage\\Constraint\\AccidentalRecreationConstraint' => __DIR__ . '/includes/editpage/Constraint/AccidentalRecreationConstraint.php',
 	'MediaWiki\\EditPage\\Constraint\\AutoSummaryMissingSummaryConstraint' => __DIR__ . '/includes/editpage/Constraint/AutoSummaryMissingSummaryConstraint.php',
 	'MediaWiki\\EditPage\\Constraint\\ChangeTagsConstraint' => __DIR__ . '/includes/editpage/Constraint/ChangeTagsConstraint.php',
@@ -3065,7 +3066,6 @@ $wgAutoloadLocalClasses = [
 	'WikitextContentHandler' => __DIR__ . '/includes/content/WikitextContentHandler.php',
 	'WikitextLogFormatter' => __DIR__ . '/includes/logging/WikitextLogFormatter.php',
 	'WinCacheBagOStuff' => __DIR__ . '/includes/libs/objectcache/WinCacheBagOStuff.php',
-	'WordAccumulator' => __DIR__ . '/includes/libs/Diff/WordAccumulator.php',
 	'WordLevelDiff' => __DIR__ . '/includes/libs/Diff/WordLevelDiff.php',
 	'WrapOldPasswords' => __DIR__ . '/maintenance/wrapOldPasswords.php',
 	'WuuConverter' => __DIR__ . '/includes/language/converters/WuuConverter.php',

includes/libs/Diff/WordAccumulator.php

@@ -111,4 +111,4 @@ class WordAccumulator {
 }
 
 /** @deprecated since 1.41 */
-class_alias( WordAccumulator::class, 'WordAccumulator' );
+class_alias( WordAccumulator::class, 'MediaWiki\\Diff\\WordAccumulator' );