tests: dumping and minimizing of script assets data

This adds a --dumptests flag to the feature_taproot.py test, to dump all its
generated test cases to files, in a format compatible with the
script_assets_test unit test. A fuzzer for said format is added as well, whose
primary purpose is coverage-based minimization of those dumps.

src/test/script_tests.cpp

@@ -1715,6 +1715,9 @@ static void AssetTest(const UniValue& test)
 
 BOOST_AUTO_TEST_CASE(script_assets_test)
 {
+    // See src/test/fuzz/script_assets_test_minimizer.cpp for information on how to generate
+    // the script_assets_test.json file used by this test.
+
     const char* dir = std::getenv("DIR_UNIT_TEST_DATA");
     BOOST_WARN_MESSAGE(dir != nullptr, "Variable DIR_UNIT_TEST_DATA unset, skipping script_assets_test");
     if (dir == nullptr) return;