Sublime: Exclude build tree from source tree project only optionally

Create a `CMAKE_SUBLIME_TEXT_2_EXCLUDE_BUILD_TREE` variable to control
addition of the build tree to `folder_exclude_patterns` in the
`.sublime-project`.  Change the default of this behavior to OFF.

Closes: #16351

Source/cmExtraSublimeTextGenerator.h

@@ -64,6 +64,8 @@ private:
 
   std::string ComputeDefines(cmSourceFile* source, cmLocalGenerator* lg,
                              cmGeneratorTarget* gtgt);
+
+  bool ExcludeBuildFolder;
 };
 
 #endif