Refactor repo contents API and add "contents-ext" API (#34822)

See the updated swagger document for details.

modules/git/tree_entry_nogogit.go

@@ -18,7 +18,7 @@ type TreeEntry struct {
 	sized     bool
 }
 
-// Name returns the name of the entry
+// Name returns the name of the entry (base name)
 func (te *TreeEntry) Name() string {
 	return te.name
 }