analysis: Add XML parsing support for unions

We can reuse the existing `Structure` parser. Currently, there are no
aliases for unions in the XML.

Author: Friz64

analysis/src/xml.rs

@@ -58,6 +58,7 @@ pub struct Registry {
     pub funcpointers: Vec<FuncPointer>,
     pub structs: Vec<Structure>,
     pub struct_aliases: Vec<Alias>,
+    pub unions: Vec<Structure>,
     pub constants: Vec<Constant>,
     pub constant_aliases: Vec<Alias>,
     pub enums: Vec<Enum>,
@@ -123,6 +124,9 @@ impl Registry {
                                 Some("struct") => {
                                     registry.structs.push(Structure::from_node(type_node, api))
                                 }
+                                Some("union") => {
+                                    registry.unions.push(Structure::from_node(type_node, api));
+                                }
                                 _ => (),
                             }
                         }