Fix develop CI: GCC 4.8, Clang 3.4 and clang-tidy errors

- unit-json_patch.cpp: move multi-line raw strings out of CHECK(), which
  GCC 4.8 cannot parse inside a macro argument
- unit-recursion_depth_limit.cpp: value-initialize the const std::hash
  (Clang 3.4 rejects default initialization of a const object)
- json_view: silence modernize-use-transparent-functors (std::less<> is
  C++14), bugprone-suspicious-stringview-data-usage (the length comes from
  the node) and the deliberate use-after-clear() / owning-memory hits in
  unit-json_view_builder.cpp; use a raw string literal there

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

tests/src/unit-recursion_depth_limit.cpp

@@ -494,7 +494,7 @@ TEST_CASE("walks over values nested around the recursion depth limit")
         for_each_value([](const std::string & kinds)
         {
             const json a = build(kinds, 1);
-            const std::hash<json> hash;
+            const std::hash<json> hash{};
             CHECK(hash(a) == hash(json(a)));
             CHECK(hash(a) == hash(json::parse(expected_compact(kinds, "1"))));
             CHECK(hash(a) != hash(build(kinds, 2)));