Follow file symlinks in the UI to their target (#28835)

Symlinks are followed when you click on a link next to an entry, either
until a file has been found or until we know that the link is dead.
When the link cannot be accessed, we fall back to the current behavior
of showing the document containing the target.

---------

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

modules/git/error.go

@@ -32,22 +32,6 @@ func (err ErrNotExist) Unwrap() error {
 	return util.ErrNotExist
 }
 
-// ErrSymlinkUnresolved entry.FollowLink error
-type ErrSymlinkUnresolved struct {
-	Name    string
-	Message string
-}
-
-func (err ErrSymlinkUnresolved) Error() string {
-	return fmt.Sprintf("%s: %s", err.Name, err.Message)
-}
-
-// IsErrSymlinkUnresolved if some error is ErrSymlinkUnresolved
-func IsErrSymlinkUnresolved(err error) bool {
-	_, ok := err.(ErrSymlinkUnresolved)
-	return ok
-}
-
 // ErrBranchNotExist represents a "BranchNotExist" kind of error.
 type ErrBranchNotExist struct {
 	Name string