Add some scaffolding for parsing affine maps:
- parsing affine map identifiers
- place-holder classes for AffineMap
- module contains a list of affine maps (defined at the top level).

PiperOrigin-RevId: 202336919
diff --git a/lib/Parser/Token.h b/lib/Parser/Token.h
index dde0722..8a654a1 100644
--- a/lib/Parser/Token.h
+++ b/lib/Parser/Token.h
@@ -34,6 +34,7 @@
     // Identifiers.
     bare_identifier,    // foo
     at_identifier,      // @foo
+    affine_map_id,      // #foo
     // TODO: @@foo, etc.
 
     integer,            // 42