update folder_depth algorithm for glob command (#13915)

# Description

This PR updates the `folder_depth` algorithm in order to make `glob` a
bit faster. The algorithm works like this. Since `folder_depth` is
always used we need to set it to a value. If the glob pattern contains
`**` then make `folder_depth` `usize::MAX`. If `--depth` is not
provided, make it 1, otherwise use the provided value.

closes #13914

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crates/nu-command/src/filesystem/glob.rs

@@ -171,8 +171,12 @@ impl Command for Glob {
 
         let folder_depth = if let Some(depth) = depth {
             depth
-        } else {
+        } else if glob_pattern.contains("**") {
             usize::MAX
+        } else if glob_pattern.contains(std::path::MAIN_SEPARATOR) {
+            glob_pattern.split(std::path::MAIN_SEPARATOR).count() + 1
+        } else {
+            1
         };
 
         let (prefix, glob) = match WaxGlob::new(&glob_pattern) {