[dnssd-server] implement DNS-SD discovery proxy functionality in core (#10050)

This commit implements a generic discovery proxy in the DNS-SD server.
It uses a set of newly added `otPlatDnssd` platform DNS-SD(mDNS) APIs
to start or stop browsers, SRV/TXT resolvers, and IPv6/IPv4 address
resolvers. These APIs closely match the native OpenThread mDNS
implementation.

OpenThread DNS-SD's existing `QueryCallback` mechanism, enabling
customized discovery proxy implementations, remains supported.

This commit includes a comprehensive unit test. This test validates
the discovery proxy's behavior, covering: standard use cases, request
timeout, s hared resolver/browser usage for multiple queries with the
same name, filtering of invalid addresses, and various edge cases.

script/check-scan-build

@@ -52,6 +52,8 @@ OT_BUILD_OPTIONS=(
     "-DOT_DHCP6_CLIENT=ON"
     "-DOT_DHCP6_SERVER=ON"
     "-DOT_DIAGNOSTIC=ON"
+    "-DOT_DNSSD_DISCOVERY_PROXY=ON"
+    "-DOT_DNSSD_SERVER=ON"
     "-DOT_DNS_CLIENT=ON"
     "-DOT_DNS_DSO=ON"
     "-DOT_ECDSA=ON"

script/make-pretty

@@ -110,6 +110,7 @@ OT_CLANG_TIDY_BUILD_OPTS=(
     '-DOT_DNS_CLIENT=ON'
     '-DOT_DNS_DSO=ON'
     '-DOT_DNS_UPSTREAM_QUERY=ON'
+    "-DOT_DNSSD_DISCOVERY_PROXY=ON"
     '-DOT_DNSSD_SERVER=ON'
     '-DOT_DUA=ON'
     '-DOT_MLR=ON'