Core: fixed memory leak on configuration reload with PCRE2.

Core: fixed memory leak on configuration reload with PCRE2.

In ngx_regex_cleanup() allocator wasn't configured when calling
pcre2_compile_context_free() and pcre2_match_data_free(), resulting
in no ngx_free() call and leaked memory.  Fix is ensure that allocator
is configured for global allocations, so that ngx_free() is actually
called to free memory.

Additionally, ngx_regex_compile_context was cleared in
ngx_regex_module_init().  It should be either not cleared, so it will
be freed by ngx_regex_cleanup(), or properly freed.  Fix is to
not clear it, so ngx_regex_cleanup() will be able to free it.

Reported by ZhenZhong Wu,
https://mailman.nginx.org/pipermail/nginx-devel/2023-September/3Z5FIKUDRN2WBSL3JWTZJ7SXDA6YIWPB.html