[Hygiene] [Mustache] rename SearchComponent to SearchBox

For consistency with VectorTabs, rename SearchComponent to only imply
component. At least two word names seems like a good target (instead of
just "Search") for grepability and standard component style conventions.

Bug: T239248
Change-Id: I1e4f7270ba29c2f35f08e92f8a28cd8a2ec8fe87

includes/VectorTemplate.php

@@ -472,6 +472,6 @@ class VectorTemplate extends BaseTemplate {
 			),
 			'searchInputLabel' => $this->getMsg( 'search' )
 		];
-		echo $templateParser->processTemplate( 'SearchComponent', $props );
+		echo $templateParser->processTemplate( 'SearchBox', $props );
 	}
 }