Reduce test suite runtime and run the Unicode tests everywhere (#5605)

Squashed onto develop from:
- Cut Unicode ill-formed byte sweeps to one representative prefix
- Pin unrelated bytes in the remaining ill-formed UTF-8 sweeps
- Speed up unit-unicode1
- Run the cheap binary format size tests unconditionally
- Compile unit-msgpack.cpp only once
- Check the JSON Pointer roundtrip for every code point again
- Cover every byte class in the ill-formed UTF-8 sweeps
- Merge the Unicode tests into unit-unicode.cpp
- Stop excluding the Unicode tests in CI

Signed-off-by: elix3r <157088510+22elix3r@users.noreply.github.com>
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-authored-by: elix3r <157088510+22elix3r@users.noreply.github.com>

tests/src/test_utils.hpp

@@ -8,6 +8,7 @@
 
 #pragma once
 
+#include <array> // array
 #include <cstdint> // uint8_t
 #include <cstddef> // size_t
 #include <fstream> // ifstream, ios
@@ -43,6 +44,33 @@ T next_integer_sample(T i, T last, T stride)
     return n < last ? n : last;
 }
 
+// UTF-8 continuation bytes in [lo, hi] that stand in for all of them in the
+// ill-formed UTF-8 tests. Both the lexer's range checks and the serializer's
+// decoder (detail::decode) only distinguish the classes 0x80..0x8F, 0x90..0x9F,
+// and 0xA0..0xBF, so the first and last byte of each class within [lo, hi]
+// exercise every behavior while a test sweeps another byte position through
+// all 256 values (#5418). Define JSON_TEST_UTF8_EXHAUSTIVE to get every byte.
+inline std::vector<int> utf8_continuation_bytes(int lo, int hi)
+{
+    std::vector<int> result;
+#ifdef JSON_TEST_UTF8_EXHAUSTIVE
+    for (int byte = lo; byte <= hi; ++byte)
+    {
+        result.push_back(byte);
+    }
+#else
+    static const std::array<int, 6> class_ends = {{0x80, 0x8F, 0x90, 0x9F, 0xA0, 0xBF}};
+    for (const int byte : class_ends)
+    {
+        if (lo <= byte && byte <= hi)
+        {
+            result.push_back(byte);
+        }
+    }
+#endif
+    return result;
+}
+
 inline std::vector<std::uint8_t> read_binary_file(const std::string& filename)
 {
     std::ifstream file(filename, std::ios::binary);