Fix the tests added by the merged PRs for all CI configurations

- discard the results of dump() and from_*() in CHECK_THROWS with
  utils::ignore_return_value (GCC -Werror=unused-result)
- give unit-bson's huge_string_t a default constructor (MSVC C2512,
  GCC 5, clang 3.5)
- unit-disabled_exceptions: use the literals namespace when the global
  UDLs are off (ci_test_noglobaludls; #5700)
- unit-binary_utf8_strict: expect the JSON pointer prefix with
  JSON_DIAGNOSTICS (#5741)
- skip the tests that rely on exceptions under JSON_NOEXCEPTION
  (#5678, #5732)
- clang-tidy and clang -Werror: static test data, CAPTURE(...);,
  const-correctness, use-after-move alias, unused conversion operator,
  a missing <iterator> include

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

tests/src/unit-bjdata.cpp

@@ -3921,7 +3921,7 @@ TEST_CASE("Universal Binary JSON Specification Examples 1")
             CHECK_NOTHROW(j = json::from_bjdata(v));
             REQUIRE(j.is_string());
             CHECK(j.get_ref<const json::string_t&>() == std::string("\xc0\xae"));
-            CHECK_THROWS_AS(j.dump(), json::type_error&);
+            CHECK_THROWS_AS(utils::ignore_return_value(j.dump()), json::type_error&);
             CHECK(json::from_bjdata(json::to_bjdata(j)) == j);
 
             // the same bytes as an object key round-trip as well