Start implementing a test suite for the CLI

We have very few tests today so this starts to add the basics of a test
suite which compiles Cargo projects on-the-fly which will hopefully help
us bolster the amount of assertions we can make about the output.

crates/cli-support/src/lib.rs

@@ -716,7 +716,7 @@ impl OutputMode {
 
     fn bundler(&self) -> bool {
         match self {
-            OutputMode::Bundler => true,
+            OutputMode::Bundler { .. } => true,
             _ => false,
         }
     }