Adds support for packaging workspaces.

Takes local dependencies into account when packaging a workspace. Builds
a temporary package registry to provide local dependencies, and overlays
it on the upstream registry.

src/bin/cargo/commands/package.rs

@@ -5,6 +5,8 @@ use cargo::ops::{self, PackageOpts};
 pub fn cli() -> Command {
     subcommand("package")
         .about("Assemble the local package into a distributable tarball")
+        .arg_index("Registry index URL to prepare the package for")
+        .arg_registry("Registry to prepare the package for")
         .arg(
             flag(
                 "list",
@@ -41,6 +43,7 @@ pub fn cli() -> Command {
 }
 
 pub fn exec(gctx: &mut GlobalContext, args: &ArgMatches) -> CliResult {
+    let reg_or_index = args.registry_or_index(gctx)?;
     let ws = args.workspace(gctx)?;
     if ws.root_maybe().is_embedded() {
         return Err(anyhow::format_err!(
@@ -64,6 +67,7 @@ pub fn exec(gctx: &mut GlobalContext, args: &ArgMatches) -> CliResult {
             jobs: args.jobs()?,
             keep_going: args.keep_going(),
             cli_features: args.cli_features()?,
+            reg_or_index,
         },
     )?;