Fix dirs removal warning (#14029)

# Description

* Primary purpose is to fix an issue with a missing escaped opening
parenthesis in the warning message when running an old `dirs` alias.
This was creating an error condition from improper interpolation.

Also

* Incorporates #13842 feedback from @kubouch by renaming `std/lib` to
`std/util`
* Removes duplication of code in `export-env`
* Renames submodule exports to `std/<submodule>` rather than
`./<submodule>` - No user-facing change other than `view files` appears
"prettier".
* In #13842, I converted the test cases to use `use std/<module>`
syntax. Previously, the tests were (effectively) using `use std *` (due
to pre-existing bugs, now fixed).

So "before", we only had test coverage on `use std *`, and "after" we
only had test coverage on `use std/<module>`. I've started adding test
cases so that we have coverage on *both* scenarios going forward.

For now, `formats` and `util` have been updated with tests for both
scenarios. I'll continue adding the others in future PRs.

# User-Facing Changes

No user-facing changes - Bug fix, refactor, and test cases only

# Tests + Formatting

- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting

Still working on updating the Doc. I ran into the `dirs` issue while
writing it and rabbit-trailed to fix it in this PR.

crates/nu-std/src/lib.rs

@@ -32,7 +32,7 @@ pub fn load_standard_library(
             ("iter", include_str!("../std/iter.nu")),
             ("log", include_str!("../std/log.nu")),
             ("math", include_str!("../std/math.nu")),
-            ("lib", include_str!("../std/lib.nu")),
+            ("util", include_str!("../std/util.nu")),
             ("xml", include_str!("../std/xml.nu")),
             // Remove in following release
             ("deprecated_dirs", include_str!("../std/deprecated_dirs.nu")),