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/unit1620.c

@@ -28,18 +28,13 @@
 
 #include "memdebug.h" /* LAST include file */
 
-static CURLcode unit_setup(void)
+static CURLcode t1620_setup(void)
 {
   CURLcode res = CURLE_OK;
   global_init(CURL_GLOBAL_ALL);
   return res;
 }
 
-static void unit_stop(void)
-{
-  curl_global_cleanup();
-}
-
 static void t1620_parse(
   const char *input,
   const char *exp_username,
@@ -74,8 +69,10 @@ static void t1620_parse(
   free(options);
 }
 
-UNITTEST_START
+static CURLcode test_unit1620(char *arg)
 {
+  UNITTEST_BEGIN(t1620_setup())
+
   CURLcode rc;
   struct Curl_easy *empty;
   enum dupstring i;
@@ -131,5 +128,5 @@ UNITTEST_START
   rc = Curl_close(&empty);
   fail_unless(rc == CURLE_OK, "Curl_close() failed");
 
+  UNITTEST_END(curl_global_cleanup())
 }
-UNITTEST_STOP