[tests] Pull out common submodules

New modules: fixture, process, program, target, and thin

tests/thin_rmap.rs

@@ -3,8 +3,11 @@ use anyhow::Result;
 mod common;
 
 use common::common_args::*;
+use common::process::*;
+use common::program::*;
+use common::target::*;
 use common::test_dir::*;
-use common::*;
+use common::thin::*;
 
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