move 'str substring' to only use ranges (#8660)

# Description

This removes all the old style of quasi-ranges before we had full range
support from `str substring`. Functionality should otherwise work, but
only with the official range syntax.

# User-Facing Changes

Removes the array and string forms of ranges from `str substring`.
Leaves only the official range support for range values.

# 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

> **Note**
> from `nushell` you can also use the `toolkit` as follows
> ```bash
> use toolkit.nu # or use an `env_change` hook to activate it
automatically
> toolkit check pr
> ```

# 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.

src/tests/test_strings.rs

@@ -3,7 +3,7 @@ use crate::tests::{fail_test, run_test, TestResult};
 #[test]
 fn cjk_in_substrings() -> TestResult {
     run_test(
-        r#"let s = '[Rust 程序设计语言](title-page.md)'; let start = ($s | str index-of '('); let end = ($s | str index-of ')'); echo ($s | str substring $"($start + 1),($end)")"#,
+        r#"let s = '[Rust 程序设计语言](title-page.md)'; let start = ($s | str index-of '('); let end = ($s | str index-of ')'); $s | str substring ($start + 1)..($end)"#,
         "title-page.md",
     )
 }