Install: Add parallel installation option

Fixes: #26000

Source/cmInstallScriptHandler.h

@@ -0,0 +1,40 @@
+/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+   file Copyright.txt or https://cmake.org/licensing for details.  */
+#pragma once
+
+#include <cstddef>
+#include <functional>
+#include <memory>
+#include <string>
+#include <vector>
+
+#include "cmUVHandlePtr.h"
+#include "cmUVProcessChain.h"
+#include "cmUVStream.h"
+
+class cmInstallScriptHandler
+{
+public:
+  cmInstallScriptHandler() = default;
+  cmInstallScriptHandler(const std::string&, std::vector<std::string>&);
+  bool isParallel();
+  int install(unsigned int j);
+  class InstallScript
+  {
+  public:
+    InstallScript(const std::vector<std::string>&);
+    void start(cm::uv_loop_ptr&, std::function<void()>);
+    void printResult(std::size_t n, std::size_t total);
+
+  private:
+    std::vector<std::string> command;
+    std::vector<std::string> output;
+    std::string name;
+    std::unique_ptr<cmUVProcessChain> chain;
+    std::unique_ptr<cmUVStreamReadHandle> streamHandler;
+    cm::uv_pipe_ptr pipe;
+  };
+
+private:
+  std::vector<std::vector<std::string>> commands;
+};