cmake: Add debugger

- Depends on cppdap and jsoncpp.
- Add --debugger argument to enable the Debugger.
- Add --debugger-pipe argument for DAP traffics over named pipes.
- Support breakpoints by filenames and line numbers.
- Support exception breakpoints.
- Call stack shows filenames and line numbers.
- Show Cache Variables.
- Show the state of currently defined targets,
  tests and directories with their properties.
- Add cmakeVersion to DAP initialize response.
- Include unit tests.

Co-authored-by: Ben McMorran <bemcmorr@microsoft.com>

Source/cmDebuggerThreadManager.h

@@ -0,0 +1,38 @@
+/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+   file Copyright.txt or https://cmake.org/licensing for details.  */
+#pragma once
+
+#include "cmConfigure.h" // IWYU pragma: keep
+
+#include <atomic>
+#include <cstdint>
+#include <list>
+#include <memory>
+#include <string>
+
+#include <cm/optional>
+
+namespace cmDebugger {
+class cmDebuggerThread;
+}
+
+namespace dap {
+struct StackTraceResponse;
+}
+
+namespace cmDebugger {
+
+class cmDebuggerThreadManager
+{
+  static std::atomic<std::int64_t> NextThreadId;
+  std::list<std::shared_ptr<cmDebuggerThread>> Threads;
+
+public:
+  cmDebuggerThreadManager() = default;
+  std::shared_ptr<cmDebuggerThread> StartThread(std::string const& name);
+  void EndThread(std::shared_ptr<cmDebuggerThread> const& thread);
+  cm::optional<dap::StackTraceResponse> GetThreadStackTraceResponse(
+    std::int64_t id);
+};
+
+} // namespace cmDebugger