Add pymdownx to l10nUtil.exe (#18882)

Fixes #18853
Summary of the issue:

pymdownx is a markdown extension we use to preserve tabs in codefenced code samples.
It is missing from being exported with l10nUtil. This results in the l10nUtil being broken.
Description of user facing changes:

l10nUtil.exe works again
Description of developer facing changes:

None
Description of development approach:

Add pymdownx to exports for l10nUtil.exe

Author: seanbudd

source/setup.py

@@ -244,6 +244,7 @@ def _genManifestTemplate(shouldHaveUIAccess: bool) -> tuple[int, int, bytes]:
 			"markdown_link_attr_modifier",
 			"mdx_truly_sane_lists",
 			"mdx_gh_links",
+			"pymdownx",
 		],
 		"includes": [
 			"nvdaBuiltin",