aconfig: improve code diffs in tests

Implement a helper function to make it easier for unit tests to diff
(and find the first difference) generated code and expected code.

Bug: 283910447
Test: atest aconfig.test
Change-Id: I460e8fbf05e8f33e8a62ecef67b2d9d77051e876

tools/aconfig/src/codegen_cpp.rs

@@ -227,8 +227,11 @@ mod tests {
         let file = generate_cpp_code(&cache).unwrap();
         assert_eq!("aconfig/com_example.h", file.path.to_str().unwrap());
         assert_eq!(
-            expect_content.replace(' ', ""),
-            String::from_utf8(file.contents).unwrap().replace(' ', "")
+            None,
+            crate::test::first_significant_code_diff(
+                expect_content,
+                &String::from_utf8(file.contents).unwrap()
+            )
         );
     }
 }