Cap RTCConfiguration certificates and enforce 32-bit overflow checks

1. Bounded the maximum number of certificates in RTCConfiguration to
   1000 to prevent reference counter overflow while maintaining ample
   headroom for legitimate multi-algorithm DTLS interoperability.
2. Updated webrtc_impl::RefCounter to declare IncRef() out-of-line
   unconditionally across all architectures.
3. Implemented RefCounter::IncRef() out-of-line in ref_counter.cc with
   an explicit RTC_CHECK_LT(prev, INT_MAX) guard on all architectures,
   preventing 32-bit integer overflow and Use-After-Free vulnerabilities
   unconditionally without causing inlined binary bloat.

Bug: chromium:513154132
Fixed: chromium:513154132
Change-Id: I9894ef08519423b24139b0250cc9da0f9737827a
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/472722
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47722}