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

docs/tests/TEST-SUITE.md

@@ -312,11 +312,9 @@ SPDX-License-Identifier: curl
 
 ### test bundles
 
-  The `--enable-test-bundles` (autotools) and `-DCURL_TEST_BUNDLES=ON` (cmake)
-  build options allow to build tests bundled into single executables, one for
-  libtests, one for unit tests and one for servers.
-  The executables' first argument is the name of libtest, unit test or server
-  respectively.
+  Individual tests are bundled into single executables, one for libtests, one
+  for unit tests and one for servers. The executables' first argument is
+  the name of libtest, unit test or server respectively.
   In these executables, the build process automatically renames the entry point
   to a unique symbol. `test` becomes `test_<tool>`, e.g. `test_lib1598` or
   `test_unit1305`. For servers `main` becomes `main_sws` for the `sws` server,