Fix passing long environment variables to the debugger

Increase the command buffer size x10 to support passing long environment
variables.  This is required in projects like GStreamer requiring to
setup env variables like GST_PLUGIN_PATH with several directories in
order to be able to debug without having to install into a prefix, which
takes a long time and slows down the development cycle.

microsoft/vscode-cpptools#8411
microsoft/vscode-cpptools#6874

Author: ylatuya

src/MICmnStreamStdin.h

@@ -55,6 +55,6 @@ class CMICmnStreamStdin : public CMICmnBase,
   CMIUtilString m_strPromptCurrent; // Command line prompt as shown to the user
   bool m_bShowPrompt; // True = Yes prompt is shown/output to the user (stdout),
                       // false = no prompt
-  static const int m_constBufferSize = 2048;
+  static const int m_constBufferSize = 20480;
   char *m_pCmdBuffer;
 };