stdlib: make the library a standalone crate (#8770)

# Description
as we now have a prelude thanks to #8627, i'd like to work on the
structure of the library 😋

and i think the first step is to make it a true standalone crate 😏

this PR
- moves all the library from `crates/nu-utils/standard_library/` to
`crates/nu-std/`
- moves the `rust` loading code from `src/run.rs` to
`crates/nu-std/src/lib.rs`

crates/nu-std/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+authors = ["The Nushell Project Developers"]
+description = "The standard library of Nushell"
+repository = "https://github.com/nushell/nushell/tree/main/crates/nu-std"
+edition = "2021"
+license = "MIT"
+name = "nu-std"
+version = "0.78.1"
+
+[dependencies]
+miette = { version = "5.6.0", features = ["fancy-no-backtrace"] }
+nu-cli = { version = "0.78.1", path = "../nu-cli" }
+nu-parser = { version = "0.78.1", path = "../nu-parser" }
+nu-protocol = { version = "0.78.1", path = "../nu-protocol" }

crates/nu-std/src/lib.rs

@@ -0,0 +1,88 @@
+use nu_cli::report_error;
+use nu_parser::{parse, parse_module_block};
+use nu_protocol::{engine::StateWorkingSet, Module, ShellError, Span};
+
+fn get_standard_library() -> &'static str {
+    include_str!("../std.nu")
+}
+
+fn load_prelude(working_set: &mut StateWorkingSet, prelude: Vec<(&str, &str)>, module: &Module) {
+    let mut decls = Vec::new();
+    let mut errs = Vec::new();
+    for (name, search_name) in prelude {
+        if let Some(id) = module.decls.get(&search_name.as_bytes().to_vec()) {
+            let decl = (name.as_bytes().to_vec(), id.to_owned());
+            decls.push(decl);
+        } else {
+            errs.push(ShellError::GenericError(
+                format!("could not load `{}` from `std`.", search_name),
+                String::new(),
+                None,
+                None,
+                Vec::new(),
+            ));
+        }
+    }
+
+    if !errs.is_empty() {
+        report_error(
+            working_set,
+            &ShellError::GenericError(
+                "Unable to load the prelude of the standard library.".into(),
+                String::new(),
+                None,
+                Some("this is a bug: please file an issue in the [issue tracker](https://github.com/nushell/nushell/issues/new/choose)".to_string()),
+                errs,
+            ),
+        );
+    }
+
+    working_set.use_decls(decls);
+}
+
+pub fn load_standard_library(
+    engine_state: &mut nu_protocol::engine::EngineState,
+) -> Result<(), miette::ErrReport> {
+    let delta = {
+        let name = "std".to_string();
+        let content = get_standard_library().as_bytes();
+
+        let mut working_set = StateWorkingSet::new(engine_state);
+
+        let start = working_set.next_span_start();
+        working_set.add_file(name.clone(), content);
+        let end = working_set.next_span_start();
+
+        let (_, module, comments) =
+            parse_module_block(&mut working_set, Span::new(start, end), name.as_bytes());
+
+        if let Some(err) = working_set.parse_errors.first() {
+            report_error(&working_set, err);
+        }
+
+        parse(&mut working_set, Some(&name), content, true);
+
+        if let Some(err) = working_set.parse_errors.first() {
+            report_error(&working_set, err);
+        }
+
+        let prelude = vec![
+            ("std help", "help"),
+            ("std help commands", "help commands"),
+            ("std help aliases", "help aliases"),
+            ("std help modules", "help modules"),
+            ("std help externs", "help externs"),
+            ("std help operators", "help operators"),
+        ];
+
+        load_prelude(&mut working_set, prelude, &module);
+
+        working_set.add_module(&name, module, comments);
+
+        working_set.render()
+    };
+
+    engine_state.merge_delta(delta)?;
+
+    Ok(())
+}