test: move and simplify BOOST_CHECK ostream helpers

Move the operator<< overloads used by BOOST_CHECK_* out of the
unit test machinery test/setup_common, into test/util/common.h.

And replace the individual per-type ToString() overloads with
a single concept-constrained template that covers any type
exposing a ToString() method. This is important to not add
uint256.h and transaction_identifier.h dependencies to the
shared test/util/common.h file.

Co-authored-by: furszy <matiasfurszyfer@protonmail.com>

src/test/script_tests.cpp

@@ -19,6 +19,7 @@
 #include <streams.h>
 #include <test/util/json.h>
 #include <test/util/random.h>
+#include <test/util/common.h>
 #include <test/util/setup_common.h>
 #include <test/util/transaction_utils.h>
 #include <util/fs.h>
@@ -26,7 +27,6 @@
 #include <util/string.h>
 
 #include <cstdint>
-#include <fstream>
 #include <string>
 #include <vector>