bpo-30947: Update libexpat from 2.2.1 to 2.2.3 (#3106)

* bpo-30947: Update libexpat from 2.2.1 to 2.2.3

* Add NEWS entry

* Add new loadlibrary.c

* expat_external.h: restore include "pyexpatns.h"

* PCbuild: add expat/loadlibrary.c

* Define XML_POOR_ENTROPY to compile expat
diff --git a/PCbuild/_elementtree.vcxproj.filters b/PCbuild/_elementtree.vcxproj.filters
index ee78295..4597ee5 100644
--- a/PCbuild/_elementtree.vcxproj.filters
+++ b/PCbuild/_elementtree.vcxproj.filters
@@ -33,6 +33,9 @@
     <ClInclude Include="..\Modules\expat\latin1tab.h">
       <Filter>Header Files</Filter>
     </ClInclude>
+    <ClInclude Include="..\Modules\expat\loadlibrary.c">
+      <Filter>Header Files</Filter>
+    </ClInclude>
     <ClInclude Include="..\Modules\expat\macconfig.h">
       <Filter>Header Files</Filter>
     </ClInclude>
@@ -69,4 +72,4 @@
       <Filter>Source Files</Filter>
     </ClCompile>
   </ItemGroup>
-</Project>
\ No newline at end of file
+</Project>