Rename CodeIndexerEnabled to IsRepoIndexerEnabled (#30762) (#30767)

Backport #30762 by @wxiaoguang

Fix  #30761

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

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

templates/repo/settings/options.tmpl

@@ -739,7 +739,7 @@
 			<form class="ui form" method="post">
 				{{.CsrfTokenHtml}}
 				<input type="hidden" name="action" value="admin_index">
-				{{if .CodeIndexerEnabled}}
+				{{if .IsRepoIndexerEnabled}}
 					<h4 class="ui header">{{ctx.Locale.Tr "repo.settings.admin_code_indexer"}}</h4>
 					<div class="inline fields">
 						<label>{{ctx.Locale.Tr "repo.settings.admin_indexer_commit_sha"}}</label>

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>