Make empty V8DebuggerId ctor public

This will allow users to create invalid V8DebuggerIds, e.g. to handle
error cases.

Bug: v8:12528
Change-Id: I6efbea934d444b520fc43531b910f4f80c718630
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3445742Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Alex Turner <alexmt@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79000}

include/v8-inspector.h

@@ -118,6 +118,7 @@ class V8_EXPORT V8ContextInfo {
 // See also Runtime.UniqueDebuggerId in the protocol.
 class V8_EXPORT V8DebuggerId {
  public:
+  V8DebuggerId() = default;
   V8DebuggerId(const V8DebuggerId&) = default;
   V8DebuggerId& operator=(const V8DebuggerId&) = default;
 
@@ -127,7 +128,6 @@ class V8_EXPORT V8DebuggerId {
 
  private:
   friend class internal::V8DebuggerId;
-  V8DebuggerId() = default;
   explicit V8DebuggerId(std::pair<int64_t, int64_t>);
 
   int64_t m_first = 0;