tests: always make bundles, adapt build and tests

Make test bundles the default. Drop non-bundle build mode.
Also do all the optimizations and tidy-ups this allows, simpler builds,
less bundle exceptions, streamlined build mechanics.

Also rework the init/deinit macro magic for unit tests. The new method
allows using unique init/deinit function names, and calling them with
arguments. This is in turn makes it possible to reduce the use of global
variables.

Note this drop existing build options `-DCURL_TEST_BUNDLES=` from cmake
and `--enable-test-bundles` / `--disable-test-bundles` from autotools.

Also:
- rename test entry functions to have unique names: `test_<testname>`
  This removes the last exception that was handled in the generator.
- fix `make dist` to not miss test sources with test bundles enabled.
- sync and merge `tests/mk-bundle.pl` into `scripts/mk-unity.pl`.
- mk-unity.pl: add `--embed` option and use it when `CURL_CLANG_TIDY=ON`
  to ensure that `clang-tidy` does not miss external test C sources.
  (because `clang-tidy` ignores code that's #included.)
- tests/unit: drop no-op setup/stop functions.
- tests: reduce symbol scopes, global macros, other fixes and tidy-ups.
- tool1621: fix to run, also fix it to pass.
- sockfilt: fix Windows compiler warning in certain unity include order,
  by explicitly including `warnless.h`.

Follow-up to 6897aeb105 #17468

Closes #17590

tests/unit/unit1323.c

@@ -25,30 +25,23 @@
 
 #include "timeval.h"
 
-static CURLcode unit_setup(void)
+static CURLcode test_unit1323(char *arg)
 {
-  return CURLE_OK;
-}
+  UNITTEST_BEGIN_SIMPLE
 
-static void unit_stop(void)
-{
+  struct a {
+    struct curltime first;
+    struct curltime second;
+    time_t result;
+  };
 
-}
-
-struct a {
-  struct curltime first;
-  struct curltime second;
-  time_t result;
-};
-
-UNITTEST_START
-{
   struct a tests[] = {
     { {36762, 8345 }, {36761, 995926 }, 13 },
     { {36761, 995926 }, {36762, 8345 }, -13 },
     { {36761, 995926 }, {0, 0}, 36761995 },
     { {0, 0}, {36761, 995926 }, -36761995 },
   };
+
   size_t i;
 
   for(i = 0; i < CURL_ARRAYSIZE(tests); i++) {
@@ -64,5 +57,6 @@ UNITTEST_START
       fail("unexpected result!");
     }
   }
+
+  UNITTEST_END_SIMPLE
 }
-UNITTEST_STOP