Add a dumb renderer to get coordinates

FlatRenderer positions items on a single row, giving each a height and width of
1.

Added getBoundingClientRect to the DOMelement which, when requested for the
first time, will place the item in with the renderer.

The goal here is to give elements a fixed position and to make it easy to map
x,y coordinates onto an element. This should work, at least with puppeteer,
since it first requests the boundingClientRect before issuing a click.

src/cdp/cdp.zig

@@ -37,6 +37,7 @@ pub const CDP = CDPT(struct {
 
 const SessionIdGen = Incrementing(u32, "SID");
 const TargetIdGen = Incrementing(u32, "TID");
+const LoaderIdGen = Incrementing(u32, "LID");
 const BrowserContextIdGen = Incrementing(u32, "BID");
 
 // Generic so that we can inject mocks into it.
@@ -54,6 +55,7 @@ pub fn CDPT(comptime TypeProvider: type) type {
         target_auto_attach: bool = false,
 
         target_id_gen: TargetIdGen = .{},
+        loader_id_gen: LoaderIdGen = .{},
         session_id_gen: SessionIdGen = .{},
         browser_context_id_gen: BrowserContextIdGen = .{},
 
@@ -183,6 +185,7 @@ pub fn CDPT(comptime TypeProvider: type) type {
                 },
                 5 => switch (@as(u40, @bitCast(domain[0..5].*))) {
                     asUint("Fetch") => return @import("domains/fetch.zig").processMessage(command),
+                    asUint("Input") => return @import("domains/input.zig").processMessage(command),
                     else => {},
                 },
                 6 => switch (@as(u48, @bitCast(domain[0..6].*))) {