Auto merge of #12262 - epage:flatten, r=weihanglo

refactor(embedded)

### What does this PR try to resolve?

This is trying to make it easier to have multiple active PRs touching `embedded.rs` by separating out the parts of the code that will be touched in each PR.  This is done by making the code roughly follow how the future code will be structured.

e.g. see #12255

### How should we test and review this PR?

Commit at a time.  This is just a refactor, so no tests are changed.

src/bin/cargo/commands/run.rs

@@ -101,8 +101,8 @@ pub fn exec_manifest_command(config: &Config, cmd: &str, args: &[OsString]) -> C
         );
     }
     let manifest_path = crate::util::try_canonicalize(manifest_path)?;
-    let script = cargo::util::toml::embedded::RawScript::parse_from(&manifest_path)?;
-    let ws = script.to_workspace(config)?;
+    let script = cargo::util::toml::embedded::parse_from(&manifest_path)?;
+    let ws = cargo::util::toml::embedded::to_workspace(&script, config)?;
 
     let mut compile_opts =
         cargo::ops::CompileOptions::new(config, cargo::core::compiler::CompileMode::Build)?;