Supply Bazel-managed CMake and Ninja for the bundled Opus build (#43083)

## Why

The bundled Opus encoder uses CMake and should not depend on tools available on a build worker's `PATH`.

## What changed

- Add `rules_foreign_cc` and provide its pinned CMake and Ninja tools and data to the `opusic-sys` build script.
- Add a CMake toolchain file that selects the declared Ninja executable, resolves the archiver path, and sets the target system and processor from `TARGET`, while retaining Bazel's compiler, SDK, and linker inputs.

GitOrigin-RevId: 48580c506d088d8c76cce958589ff94da458bd79

third_party/voice/BUILD.bazel

@@ -1,4 +1,6 @@
 # All native build consumers must receive the same pinned source manifest.
+exports_files(["opus-toolchain.cmake"])
+
 filegroup(
     name = "source_inputs",
     srcs = [

third_party/voice/opus-toolchain.cmake

@@ -0,0 +1,14 @@
+# CMake's generator must use the Ninja declared in the Bazel action.
+set(CMAKE_MAKE_PROGRAM "$ENV{CODEX_VOICE_NINJA}" CACHE FILEPATH "" FORCE)
+# Archiver paths from Bazel are relative to the execution root.
+get_filename_component(CMAKE_AR "$ENV{AR}" ABSOLUTE
+    BASE_DIR "${CMAKE_CURRENT_LIST_DIR}/../..")
+if("$ENV{TARGET}" MATCHES "apple-darwin$")
+  set(CMAKE_SYSTEM_NAME Darwin)
+elseif("$ENV{TARGET}" MATCHES "windows")
+  set(CMAKE_SYSTEM_NAME Windows)
+else()
+  set(CMAKE_SYSTEM_NAME Linux)
+endif()
+string(REGEX REPLACE "-.*" "" CMAKE_SYSTEM_PROCESSOR "$ENV{TARGET}")
+# Compiler, SDK and linker inputs remain supplied by Bazel's target toolchain.