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/examples/CMakeLists.txt

@@ -24,7 +24,7 @@
 
 add_custom_target(curl-examples)
 
-# Get 'check_PROGRAMS' variable
+# Get check_PROGRAMS variable
 curl_transform_makefile_inc("Makefile.inc" "${CMAKE_CURRENT_BINARY_DIR}/Makefile.inc.cmake")
 include("${CMAKE_CURRENT_BINARY_DIR}/Makefile.inc.cmake")
 
@@ -37,7 +37,6 @@ foreach(_target IN LISTS check_PROGRAMS)
   if(LIB_SELECTED STREQUAL LIB_STATIC AND WIN32)
     set_property(TARGET ${_target_name} APPEND PROPERTY COMPILE_DEFINITIONS "CURL_STATICLIB")
   endif()
-  set_target_properties(${_target_name} PROPERTIES
-    OUTPUT_NAME "${_target}" UNITY_BUILD OFF
-    PROJECT_LABEL "Example ${_target}")
+  set_target_properties(${_target_name} PROPERTIES OUTPUT_NAME "${_target}" PROJECT_LABEL "Example ${_target}"
+    UNITY_BUILD OFF)
 endforeach()

docs/examples/Makefile.am

@@ -57,7 +57,7 @@ LDADD = $(LIBDIR)/libcurl.la @LIBCURL_PC_LIBS_PRIVATE@
 # This might hold -Werror
 CFLAGS += @CURL_CFLAG_EXTRAS@
 
-# Makefile.inc provides the check_PROGRAMS and COMPLICATED_EXAMPLES defines
+# Get check_PROGRAMS variable
 include Makefile.inc
 
 all: $(check_PROGRAMS)

docs/examples/Makefile.inc

@@ -21,6 +21,7 @@
 # SPDX-License-Identifier: curl
 #
 ###########################################################################
+# Shared between CMakeLists.txt and Makefile.am
 
 # These are all libcurl example programs to be test compiled
 check_PROGRAMS = \