Unify search boxes (#29530)

Unify all but a few search boxes to use uniform style, uniform
translations and shared templates where possible.
Remove a few duplicated search templates, e. g. code search.

<details><summary>Example after screenshots:</summary>

![grafik](e20e7d6b-c6be-4a47-b132-672766f41421)

![grafik](d5b11b9c-c12f-4a29-8fb0-24e5aa511d18)

![grafik](d86bb444-36c7-426d-9cf1-c634963dffb1)

![grafik](a76c0319-0518-484a-a840-563d02b61198)

</details>

Also includes #29700

Co-authored-by: 6543 <6543@obermui.de>

---------

Co-authored-by: 6543 <m.huber@kithara.com>
Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Giteabot <teabot@gitea.io>
Conflicts:
	routers/web/repo/search.go
	templates/repo/home.tmpl
	templates/repo/search.tmpl
	templates/shared/repo_search.tmpl

routers/web/repo/commit.go

@@ -203,7 +203,7 @@ func SearchCommits(ctx *context.Context) {
 
 	ctx.Data["Keyword"] = query
 	if all {
-		ctx.Data["All"] = "checked"
+		ctx.Data["All"] = true
 	}
 	ctx.Data["Username"] = ctx.Repo.Owner.Name
 	ctx.Data["Reponame"] = ctx.Repo.Repository.Name