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/runtests.pl

@@ -882,7 +882,6 @@ sub checksystemfeatures {
     logmsg sprintf("* Env: %s%s%s%s%s", $valgrind?"Valgrind ":"",
                    $run_duphandle?"test-duphandle ":"",
                    $run_event_based?"event-based ":"",
-                   $bundle?"bundle ":"",
                    $nghttpx_h3);
     logmsg sprintf("%s\n", $libtool?"Libtool ":"");
     logmsg ("* Seed: $randseed\n");
@@ -2503,15 +2502,6 @@ EOHELP
     shift @ARGV;
 }
 
-# Detect a test bundle build.
-# Do not look for 'tunits' and 'units' because not all configurations build them.
-if(-e $LIBDIR . "libtests" . exe_ext('TOOL') &&
-   -e $SRVDIR . "servers" . exe_ext('SRV')) {
-    # use test bundles
-    $bundle=1;
-    $ENV{'CURL_TEST_BUNDLES'} = 1;
-}
-
 delete $ENV{'DEBUGINFOD_URLS'} if($ENV{'DEBUGINFOD_URLS'} && $no_debuginfod);
 
 if(!$randseed) {