Implement macOS system proxy resolution in utility process

Replace NOTIMPLEMENTED stubs in the utility-process mac proxy resolver
with a working implementation that queries macOS SystemConfiguration and
CFNetwork frameworks.

MacAPIWrapperImpl now calls SCDynamicStoreCopyProxies() and
CFNetworkCopyProxiesForURL() (with ws/wss scheme rewriting).
MacSystemProxyResolverImpl::GetProxyForUrl() parses the returned CFArray
of proxy dictionaries into a net::ProxyList, handling HTTP, HTTPS,
SOCKS, and DIRECT entry types.

PAC configurations (both kCFProxyTypeAutoConfigurationURL and
kCFProxyTypeAutoConfigurationJavaScript) are explicitly rejected with
kCFNetworkExecutePacScriptFailed since PAC script execution is not yet
supported and will be added in a follow-up CL.

Also adds kCFNetworkResolutionError to MacProxyResolutionStatus to
distinguish CFNetwork failures from SystemConfiguration failures,
improving diagnostics.

Bug: 442313607
Change-Id: I3d45b3a1b3b346fe995bddac8f2b58636f32f694
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7557781
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Commit-Queue: krishna dheeraj Pannala <kpannala@microsoft.com>
Reviewed-by: Hayato Ito <hayato@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1589291}
NOKEYCHECK=True
GitOrigin-RevId: 705906db3b7c4ce81f121d2ec6484bd254ccdebd