Introduce grpc_completion_queue_factory API

Just the API and a bare-bone implementation
diff --git a/vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj.filters b/vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj.filters
index 414e2a5..b8ad369 100644
--- a/vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj.filters
+++ b/vsprojects/vcxproj/grpc_unsecure/grpc_unsecure.vcxproj.filters
@@ -313,6 +313,9 @@
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\surface\completion_queue.c">
       <Filter>src\core\lib\surface</Filter>
     </ClCompile>
+    <ClCompile Include="$(SolutionDir)\..\src\core\lib\surface\completion_queue_factory.c">
+      <Filter>src\core\lib\surface</Filter>
+    </ClCompile>
     <ClCompile Include="$(SolutionDir)\..\src\core\lib\surface\event_string.c">
       <Filter>src\core\lib\surface</Filter>
     </ClCompile>
@@ -956,6 +959,9 @@
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\surface\completion_queue.h">
       <Filter>src\core\lib\surface</Filter>
     </ClInclude>
+    <ClInclude Include="$(SolutionDir)\..\src\core\lib\surface\completion_queue_factory.h">
+      <Filter>src\core\lib\surface</Filter>
+    </ClInclude>
     <ClInclude Include="$(SolutionDir)\..\src\core\lib\surface\event_string.h">
       <Filter>src\core\lib\surface</Filter>
     </ClInclude>