Add wxProcess::SetPriority() to allow setting the priority of child processes.

This uses the same conventions as wxThread::SetPriority() but works on the
entire process.

Closes #14931.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73406 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/process.h

@@ -104,6 +104,15 @@ public:
                         wxInputStream *errStream);
 #endif // wxUSE_STREAMS
 
+    // priority
+        // Sets the priority to the given value: see wxPRIORITY_XXX constants.
+        //
+        // NB: the priority can only be set before the process is created
+    void SetPriority(unsigned priority);
+
+        // Get the current priority.
+    unsigned GetPriority() const { return m_priority; }
+
     // implementation only - don't use!
     // --------------------------------
 
@@ -116,6 +125,8 @@ protected:
     int m_id;
     long m_pid;
 
+    unsigned m_priority;
+
 #if wxUSE_STREAMS
     // these streams are connected to stdout, stderr and stdin of the child
     // process respectively (yes, m_inputStream corresponds to stdout -- very