Tweak generate.Tuple and generate.Union

Leverage comptime fields to give generated Tuple a default value, allowing
TupleT and Tuple to be merged.

Only call generate.Tuple on the final output. This eliminates redundant
deduplication, and results in a simpler API (nested types just need to expose
a natural Zig tuple).

generate.Union leverages the new Tuple and removes unused features.

src/html/elements.zig

@@ -99,9 +99,8 @@ pub const Interfaces = .{
     HTMLVideoElement,
     CSSProperties,
 };
-const Generated = generate.Union.compile(Interfaces);
-pub const Union = Generated._union;
-pub const Tags = Generated._enum;
+
+pub const Union = generate.Union(Interfaces);
 
 // Abstract class
 // --------------

src/html/html.zig

@@ -25,7 +25,7 @@ const Navigator = @import("navigator.zig").Navigator;
 const History = @import("history.zig").History;
 const Location = @import("location.zig").Location;
 
-pub const Interfaces = generate.Tuple(.{
+pub const Interfaces = .{
     HTMLDocument,
     HTMLElem.HTMLElement,
     HTMLElem.HTMLMediaElement,
@@ -34,4 +34,4 @@ pub const Interfaces = generate.Tuple(.{
     Navigator,
     History,
     Location,
-});
+};