[libc][docs] Add nl_types.h POSIX header documentation (#122006) (#194373)

Add nl_types.h implementation-status docs to llvm-libc.

Depends on PR #194367. That change fixes docgen lookup for underscored
headers, without it, the macros of nl_types.h implementation status is
not reported accurately.

libc/docs/CMakeLists.txt

@@ -54,6 +54,7 @@ if (SPHINX_FOUND)
       glob
       inttypes
       locale
+      nl_types
       net/if
       netinet/in
       poll

libc/docs/headers/index.rst

@@ -23,6 +23,7 @@ Implementation Status
    math/index.rst
    net/if
    netinet/in
+   nl_types
    poll
    search
    setjmp

libc/utils/docgen/nl_types.yaml

@@ -0,0 +1,13 @@
+functions:
+  catclose:
+    in-latest-posix: ""
+  catgets:
+    in-latest-posix: ""
+  catopen:
+    in-latest-posix: ""
+
+macros:
+  NL_CAT_LOCALE:
+    in-latest-posix: ""
+  NL_SETD:
+    in-latest-posix: ""