enhance(repo): prefill new issue and pull request sidebars from query parameters (#39804)

Links to the new issue and new pull request pages can preselect sidebar
values with the same query parameters as the issue list filters:
`labels`, `milestone`, `project` and `assignee`, each taking
comma-separated IDs, e.g. `compare/main...branch?labels=1,2&assignee=3`.
Previously, pull requests supported none of them and issues only
`milestone` and `project`. On the compare page they also expand the new
pull request form, like `title` and `body`. Query values take precedence
over issue template labels and assignees.

* Fix https://github.com/go-gitea/gitea/issues/27341

---------

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

modules/base/tool.go

@@ -12,6 +12,7 @@ import (
 	"fmt"
 	"hash"
 	"strconv"
+	"strings"
 	"time"
 
 	"gitea.dev/modules/setting"
@@ -117,3 +118,7 @@ func Int64sToStrings(ints []int64) []string {
 	}
 	return strs
 }
+
+func JoinInt64s(ints []int64, sep string) string {
+	return strings.Join(Int64sToStrings(ints), sep)
+}