Add decimals to int when using into string --decimals (#6085)

* Add decimals to int when using `into string --decimals`

* Add tests for `into string` when converting int with `--decimals`

* Apply formatting

* Merge `into_str` test files

* Comment out unused code and add TODOs

* Use decimal separator depending on system locale

* Add test helper to run closure in different locale

* Add tests for int-to-string conversion using different locales

* Add utils function to get system locale

* Add panic message when locking mutex fails

* Catch and resume panic later to prevent Mutex poisoning when test fails

* Move test to `nu-test-support` to keep `nu-utils` free of `nu-*` dependencies

See https://github.com/nushell/nushell/pull/6085#issuecomment-1193131694

* Rename test support fn `with_fake_locale` to `with_locale_override`

* Move `get_system_locale()` to `locale` module

* Allow overriding locale with special env variable (when not in release)

* Use special env var to override locale during testing

* Allow callback to return a value in `with_locale_override()`

* Allow multiple options in `nu!` macro

* Allow to set locale as `nu!` macro option

* Use new `locale` option of `nu!` macro instead of `with_locale_override`

Using the `locale` options does not lock the `LOCALE_OVERRIDE_MUTEX`
mutex in `nu-test-support::locale_override` but instead calls the `nu`
command directly with the `NU_LOCALE_OVERRIDE` environment variable.
This allows for parallel test excecution.

* Fix: Add option identifier for `cwd` in usage of `nu!` macro

* Rely on `Display` trait for formatting `nu!` macro command

- Removed the `DisplayPath` trait
- Implement `Display` for `AbsolutePath`, `RelativePath` and
  `AbsoluteFile`

* Default to locale `en_US.UTF-8` for tests when using `nu!` macro

* Add doc comment to `nu!` macro

* Format code using `cargo fmt --all`

* Pass function directly instead of wrapping the call in a closure

https://rust-lang.github.io/rust-clippy/master/index.html#redundant_closure

* Pass function to `or_else()` instead of calling it inside `or()`

https://rust-lang.github.io/rust-clippy/master/index.html#or_fun_call

* Fix: Add option identifier for `cwd` in usage of `nu!` macro

crates/nu-utils/src/lib.rs

@@ -1,5 +1,7 @@
+pub mod locale;
 pub mod utils;
 
+pub use locale::get_system_locale;
 pub use utils::{
     enable_vt_processing, get_default_config, get_default_env, get_ls_colors,
     stderr_write_all_and_flush, stdout_write_all_and_flush,

crates/nu-utils/src/locale.rs

@@ -0,0 +1,39 @@
+use num_format::Locale;
+
+#[cfg(debug_assertions)]
+pub const LOCALE_OVERRIDE_ENV_VAR: &str = "NU_TEST_LOCALE_OVERRIDE";
+
+pub fn get_system_locale() -> Locale {
+    let locale_string = get_system_locale_string().unwrap_or_else(|| String::from("en-US"));
+    // Since get_locale() and Locale::from_name() don't always return the same items
+    // we need to try and parse it to match. For instance, a valid locale is de_DE
+    // however Locale::from_name() wants only de so we split and parse it out.
+    let locale_string = locale_string.replace('_', "-"); // en_AU -> en-AU
+
+    match Locale::from_name(&locale_string) {
+        Ok(loc) => loc,
+        _ => {
+            let all = num_format::Locale::available_names();
+            let locale_prefix = &locale_string.split('-').collect::<Vec<&str>>();
+            if all.contains(&locale_prefix[0]) {
+                // eprintln!("Found alternate: {}", &locale_prefix[0]);
+                Locale::from_name(locale_prefix[0]).unwrap_or(Locale::en)
+            } else {
+                // eprintln!("Unable to find matching locale. Defaulting to en-US");
+                Locale::en
+            }
+        }
+    }
+}
+
+#[cfg(debug_assertions)]
+fn get_system_locale_string() -> Option<String> {
+    std::env::var(LOCALE_OVERRIDE_ENV_VAR)
+        .ok()
+        .or_else(sys_locale::get_locale)
+}
+
+#[cfg(not(debug_assertions))]
+fn get_system_locale_string() -> Option<String> {
+    sys_locale::get_locale()
+}