Expose filtering by file type in glob (#7834)

# Description

Add flags for filtering the output of `glob` by file type. I find myself
occasionally wanting to do this, and getting a file's
[file_type](https://docs.rs/wax/latest/wax/struct.WalkEntry.html#method.file_type)
is presumably fast to do as it doesn't have to go through the fallible
metadata method.

The design of the signature does concern me; it's not as readable as a
filter or "include" type list would be. They have to be filtered one by
one, which can be annoying if you only want files `-D -S`, or only want
folders `-F -S`, or only want symlinks `--butwhy?`. I considered
SyntaxShape::Keyword for this but I'll just defer to comments on this PR
if they pop up.

I'd also like to bring up performance since including these flags
technically incurs a `.filter` penalty on all glob calls, which could be
optimized out if we added a branch for the no-filters case. But in
reality I'd expect the file system to be the bottleneck and the flags to
be pretty branch predictor friendly, so eh

# User-Facing Changes
Three new flags when using `glob` and a slightly more cluttered help
page. No breaking changes, I hope.

# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

crates/nu-command/tests/commands/glob.rs

@@ -37,3 +37,84 @@ fn nonempty_glob_lists_matching_paths() {
         assert_eq!(actual.out, "3");
     })
 }
+
+#[test]
+fn glob_subdirs() {
+    Playground::setup("glob_subdirs", |dirs, sandbox| {
+        sandbox.with_files(vec![
+            EmptyFile("yehuda.txt"),
+            EmptyFile("jonathan.txt"),
+            EmptyFile("andres.txt"),
+        ]);
+        sandbox.mkdir("children");
+        sandbox.within("children").with_files(vec![
+            EmptyFile("timothy.txt"),
+            EmptyFile("tiffany.txt"),
+            EmptyFile("trish.txt"),
+        ]);
+
+        let actual = nu!(
+            cwd: dirs.test(),
+            pipeline("glob '**/*' | length"),
+        );
+
+        assert_eq!(
+            actual.out, "8",
+            "count must be 8 due to 6 files and 2 folders, including the cwd"
+        );
+    })
+}
+
+#[test]
+fn glob_subdirs_ignore_dirs() {
+    Playground::setup("glob_subdirs_ignore_directories", |dirs, sandbox| {
+        sandbox.with_files(vec![
+            EmptyFile("yehuda.txt"),
+            EmptyFile("jonathan.txt"),
+            EmptyFile("andres.txt"),
+        ]);
+        sandbox.mkdir("children");
+        sandbox.within("children").with_files(vec![
+            EmptyFile("timothy.txt"),
+            EmptyFile("tiffany.txt"),
+            EmptyFile("trish.txt"),
+        ]);
+
+        let actual = nu!(
+            cwd: dirs.test(),
+            pipeline("glob '**/*' -D | length"),
+        );
+
+        assert_eq!(
+            actual.out, "6",
+            "directory count must be 6, ignoring the cwd and the children folders"
+        );
+    })
+}
+
+#[test]
+fn glob_ignore_files() {
+    Playground::setup("glob_ignore_files", |dirs, sandbox| {
+        sandbox.with_files(vec![
+            EmptyFile("yehuda.txt"),
+            EmptyFile("jonathan.txt"),
+            EmptyFile("andres.txt"),
+        ]);
+        sandbox.mkdir("children");
+        sandbox.within("children").with_files(vec![
+            EmptyFile("timothy.txt"),
+            EmptyFile("tiffany.txt"),
+            EmptyFile("trish.txt"),
+        ]);
+
+        let actual = nu!(
+            cwd: dirs.test(),
+            pipeline("glob '*' -F | length"),
+        );
+
+        assert_eq!(
+            actual.out, "1",
+            "should only find one folder; ignoring cwd, files, subfolders"
+        );
+    })
+}