Rename CodeIndexerEnabled to IsRepoIndexerEnabled (#30762)

Fix  #30761

Most places use `IsRepoIndexerEnabled` but not `CodeIndexerEnabled`, so
it should always use `IsRepoIndexerEnabled` for consistency.

templates/shared/search/code/search.tmpl

@@ -8,7 +8,7 @@
 			<p>{{ctx.Locale.Tr "search.code_search_unavailable"}}</p>
 		</div>
 	{{else}}
-		{{if not .CodeIndexerEnabled}}
+		{{if not .IsRepoIndexerEnabled}}
 			<div class="ui message">
 				<p>{{ctx.Locale.Tr "search.code_search_by_git_grep"}}</p>
 			</div>