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/serverhelp.pm

@@ -247,14 +247,7 @@ sub server_exe {
     if(!defined $ext) {
         $ext = 'SRV';
     }
-    my $cmd;
-    if($ENV{'CURL_TEST_BUNDLES'}) {
-        $cmd = $SRVDIR . "servers" . exe_ext($ext) . " $name";
-    }
-    else {
-        $cmd = $SRVDIR . $name . exe_ext($ext);
-    }
-    return exerunner() . "$cmd";
+    return exerunner() . $SRVDIR . "servers" . exe_ext($ext) . " $name";
 }
 
 
@@ -266,13 +259,7 @@ sub server_exe_args {
     if(!defined $ext) {
         $ext = 'SRV';
     }
-    my @cmd;
-    if($ENV{'CURL_TEST_BUNDLES'}) {
-        @cmd = ($SRVDIR . "servers" . exe_ext($ext), $name);
-    }
-    else {
-        @cmd = ($SRVDIR . $name . exe_ext($ext));
-    }
+    my @cmd = ($SRVDIR . "servers" . exe_ext($ext), $name);
     if($ENV{'CURL_TEST_EXE_RUNNER'}) {
         unshift @cmd, $ENV{'CURL_TEST_EXE_RUNNER'};
     }