[ruby] Fix compilation errors on clang 16

[stanhu]

As announced in https://discourse.llvm.org/t/clang-16-notice-of-potentially-breaking-changes/65562, clang 16 defaults -Wincompatible-function-pointer-types to be on. This causes a number of hard errors due to implicit conversions between void * and void, such as:

../../../../src/ruby/ext/grpc/rb_channel.c:770:47: error: incompatible function pointer types passing 'VALUE (VALUE)' (aka 'unsigned long (unsigned long)') to parameter of type 'VALUE (*)(void *)' (aka 'unsigned long (*)(void *)') [-Wincompatible-function-pointer-types]
  g_channel_polling_thread = rb_thread_create(run_poll_channels_loop, NULL);
                                              ^~~~~~~~~~~~~~~~~~~~~~
/root/.rbenv/versions/3.1.4/include/ruby-3.1.0/ruby/internal/intern/thread.h:190:32: note: passing argument to parameter 'f' here
VALUE rb_thread_create(VALUE (*f)(void *g), void *g);
                               ^
../../../../src/ruby/ext/grpc/rb_channel.c:780:41: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
void grpc_rb_channel_polling_thread_stop() {
                                        ^
                                         void
../../../../src/ruby/ext/grpc/rb_channel.c:786:30: error: incompatible function pointer types passing 'void (void *)' to parameter of type 'void *(*)(void *)' [-Wincompatible-function-pointer-types]
  rb_thread_call_without_gvl(run_poll_channels_loop_unblocking_func, NULL, NULL,

This commit fixes these pointer types using wrapper functions where necessary.

This issue was also raised on the FreeBSD port of the grpc gem: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=271540

[stanhu]

@alto-ruby @veblush Homebrew users of clang 16 found that grpc fails to build without this change. I see that #32920 adds CI support for clang 16.

[alto-ruby]

LGTM.
@apolcyn could you take a look as well?
@stanhu thanks for the PR, could you rebase to the latest master?

[alto-ruby]

Sanity checks failed with formatting errors: https://source.cloud.google.com/results/invocations/8143196f-0e53-4d33-a1a6-63577c48f97a/targets/github%2Fgrpc%2Frun_tests%2Fsanity_linux_dbg_native%2Ftools%2Fdistrib%2Fclang_format_code.sh/tests

If you have trouble running the clangformat script, format in vscode would works well.

[alto-ruby]

@apolcyn Hi Alex do you have comments? Could we get your approval of this PR?
I'll wait one more week to see if you have any concerns, if not, I'll go ahead and merge it. Sounds OK?

[HannahShiSFB]

@sampajano Hi Eryu, could you help me check the "import/copybara Pending" status? Thanks a lot!

[sampajano]

@HannahShiSFB Thanks for checking! I've approved the internal merge request and will find one more reviewer to approve too (2 is required)!