Subtree memorization / reactive templates (#488)

This commit adds subtree memoization to Dioxus.

Subtree memoization is basically a compile-time step that drastically 
reduces the amount of work the diffing engine needs to do at runtime by
extracting non-changing nodes out into a static "template." Templates 
are then understood by the various renderers in the ecosystem as a 
faster way of rendering the same items. 

For example, in the web, templates are simply a set of DOM Nodes created 
once and then cloned later. This is the same pattern frameworks like Lithtml
and SolidJS use to achieve near-perfect performance. 

Subtree memoization adds an additional level of complexity to Dioxus. The RSX
macro needs to be much smarter to identify changing/nonchanging nodes and
generate a mapping between the Template and its runtime counterparts.

This commit represents a working starter point for this work, adding support 
for templates for the web, desktop, liveview, ssr, and native-core renderers.
In the future we will try to shrink code generation, generally improve 
performance, and simplify our implementation.

packages/liveview/src/events.rs

@@ -5,7 +5,8 @@
 use std::any::Any;
 use std::sync::Arc;
 
-use dioxus_core::{ElementId, EventPriority, UserEvent};
+use dioxus_core::GlobalNodeId;
+use dioxus_core::{EventPriority, UserEvent};
 use dioxus_html::event_bubbles;
 use dioxus_html::on::*;
 
@@ -25,7 +26,7 @@ pub(crate) fn parse_ipc_message(payload: &str) -> Option<IpcMessage> {
 #[derive(serde::Serialize, serde::Deserialize)]
 struct ImEvent {
     event: String,
-    mounted_dom_id: u64,
+    mounted_dom_id: GlobalNodeId,
     contents: serde_json::Value,
 }
 
@@ -36,7 +37,7 @@ pub fn trigger_from_serialized(val: serde_json::Value) -> UserEvent {
         contents,
     } = serde_json::from_value(val).unwrap();
 
-    let mounted_dom_id = Some(ElementId(mounted_dom_id as usize));
+    let mounted_dom_id = Some(mounted_dom_id);
 
     let name = event_name_from_type(&event);
     let event = make_synthetic_event(&event, contents);