Use frontend fetch for branch dropdown component (#25719)

- Send request to get branch/tag list, use loading icon when waiting for
response.
- Only fetch when the first time branch/tag list shows.
- For backend, removed assignment to `ctx.Data["Branches"]` and
`ctx.Data["Tags"]` from `context/repo.go` and passed these data wherever
needed.
- Changed some `v-if` to `v-show` and used native `svg` as mentioned in
https://github.com/go-gitea/gitea/pull/25719#issuecomment-1631712757 to
improve perfomance when there are a lot of branches.
- Places Used the dropdown component:

     Repo Home Page
    
<img width="1429" alt="Screen Shot 2023-07-06 at 12 17 51"
src="https://github.com/go-gitea/gitea/assets/17645053/6accc7b6-8d37-4e88-ae1a-bd2b3b927ea0">

    Commits Page

<img width="1431" alt="Screen Shot 2023-07-06 at 12 18 34"
src="https://github.com/go-gitea/gitea/assets/17645053/2d0bf306-d1e2-45a8-a784-bc424879f537">

    Specific commit -> operations -> cherry-pick
    
<img width="758" alt="Screen Shot 2023-07-06 at 12 23 28"
src="https://github.com/go-gitea/gitea/assets/17645053/1e557948-3881-4e45-a625-8ef36d45ae2d">

    Release Page
    
<img width="1433" alt="Screen Shot 2023-07-06 at 12 25 05"
src="https://github.com/go-gitea/gitea/assets/17645053/3ec82af1-15a4-4162-a50b-04a9502161bb">

- Demo


https://github.com/go-gitea/gitea/assets/17645053/d45d266b-3eb0-465a-82f9-57f78dc5f9f3

- Note:

UI of dropdown menu could be improved in another PR as it should apply
to more dropdown menus.

Fix #14180

---------

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

routers/web/repo/repo.go

@@ -622,3 +622,64 @@ func SearchRepo(ctx *context.Context) {
 		Data: results,
 	})
 }
+
+type branchTagSearchResponse struct {
+	Results []string `json:"results"`
+}
+
+// GetBranchesList get branches for current repo'
+func GetBranchesList(ctx *context.Context) {
+	branchOpts := git_model.FindBranchOptions{
+		RepoID:          ctx.Repo.Repository.ID,
+		IsDeletedBranch: util.OptionalBoolFalse,
+		ListOptions: db.ListOptions{
+			ListAll: true,
+		},
+	}
+	branches, err := git_model.FindBranchNames(ctx, branchOpts)
+	if err != nil {
+		ctx.JSON(http.StatusInternalServerError, err)
+		return
+	}
+	resp := &branchTagSearchResponse{}
+	// always put default branch on the top if it exists
+	if util.SliceContains(branches, ctx.Repo.Repository.DefaultBranch) {
+		branches = util.SliceRemoveAll(branches, ctx.Repo.Repository.DefaultBranch)
+		branches = append([]string{ctx.Repo.Repository.DefaultBranch}, branches...)
+	}
+	resp.Results = branches
+	ctx.JSON(http.StatusOK, resp)
+}
+
+// GetTagList get tag list for current repo
+func GetTagList(ctx *context.Context) {
+	tags, err := repo_model.GetTagNamesByRepoID(ctx, ctx.Repo.Repository.ID)
+	if err != nil {
+		ctx.JSON(http.StatusInternalServerError, err)
+		return
+	}
+	resp := &branchTagSearchResponse{}
+	resp.Results = tags
+	ctx.JSON(http.StatusOK, resp)
+}
+
+func PrepareBranchList(ctx *context.Context) {
+	branchOpts := git_model.FindBranchOptions{
+		RepoID:          ctx.Repo.Repository.ID,
+		IsDeletedBranch: util.OptionalBoolFalse,
+		ListOptions: db.ListOptions{
+			ListAll: true,
+		},
+	}
+	brs, err := git_model.FindBranchNames(ctx, branchOpts)
+	if err != nil {
+		ctx.ServerError("GetBranches", err)
+		return
+	}
+	// always put default branch on the top if it exists
+	if util.SliceContains(brs, ctx.Repo.Repository.DefaultBranch) {
+		brs = util.SliceRemoveAll(brs, ctx.Repo.Repository.DefaultBranch)
+		brs = append([]string{ctx.Repo.Repository.DefaultBranch}, brs...)
+	}
+	ctx.Data["Branches"] = brs
+}