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
diff --git a/tools/aconfig/Cargo.toml b/tools/aconfig/Cargo.toml
index 8517dd2..b3c73b8 100644
--- a/tools/aconfig/Cargo.toml
+++ b/tools/aconfig/Cargo.toml
@@ -18,3 +18,6 @@
 
 [build-dependencies]
 protobuf-codegen = "3.2.0"
+
+[dev-dependencies]
+itertools = "0.10.5"