[nat64] implement nat64 translator (ot::Nat64::Translator) (#7836)

This commit:

- implements the core logic for translating packets for NAT64,
  including the public APIs exposed to platform daemons.

- includes changes for POSIX platform, use `OT_POSIX_NAT64_CIDR`,
  `OPENTHREAD_POSIX_CONFIG_NAT64_CIDR` for setting the CIDR for NAT64
  during build time.

- exposes `otNat64Send(otInstance *aInstance, otMessage *aMessage)`
  and `void otNat64SetReceiveIp4Callback(otInstance *aInstance,
  otNat64ReceiveIp4Callback aCallback, void *aContext)`.

script/check-scan-build

@@ -38,6 +38,7 @@ readonly OT_BUILD_OPTIONS=(
     "-DOT_BORDER_ROUTER=ON"
     "-DOT_BORDER_ROUTING=ON"
     "-DOT_BORDER_ROUTING_NAT64=ON"
+    "-DOT_NAT64_TRANSLATOR=ON"
     "-DOT_COAP=ON"
     "-DOT_COAP_BLOCK=ON"
     "-DOT_COAP_OBSERVE=ON"

script/check-simulation-build-autotools

@@ -95,6 +95,8 @@ build_all_features()
 
     local options_1_3=(
         "-DOPENTHREAD_CONFIG_BACKBONE_ROUTER_ENABLE=1"
+        "-DOPENTHREAD_CONFIG_BORDER_ROUTING_NAT64_ENABLE=1"
+        "-DOPENTHREAD_CONFIG_NAT64_TRANSLATOR_ENABLE=1"
         "-DOPENTHREAD_CONFIG_MAC_CSL_RECEIVER_ENABLE=1"
         "-DOPENTHREAD_CONFIG_DUA_ENABLE=1"
         "-DOPENTHREAD_CONFIG_MLR_ENABLE=1"

script/check-simulation-build-cmake

@@ -57,6 +57,8 @@ build_all_features()
     local options=(
         "-DOT_BACKBONE_ROUTER=ON"
         "-DOT_BORDER_ROUTING=ON"
+        "-DOT_BORDER_ROUTING_NAT64=ON"
+        "-DOT_NAT64_TRANSLATOR=ON"
         "-DOT_CSL_RECEIVER=ON"
         "-DOT_MLR=ON"
         "-DOT_OTNS=ON"

script/make-pretty

@@ -84,6 +84,7 @@ readonly OT_CLANG_TIDY_BUILD_OPTS=(
     '-DOT_BORDER_ROUTER=ON'
     '-DOT_BORDER_ROUTING=ON'
     '-DOT_BORDER_ROUTING_NAT64=ON'
+    '-DOT_NAT64_TRANSLATOR=ON'
     '-DOT_CHANNEL_MANAGER=ON'
     '-DOT_CHANNEL_MONITOR=ON'
     '-DOT_CHILD_SUPERVISION=ON'