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/rsx/src/node.rs

@@ -16,11 +16,11 @@ Parse
 -> "text {with_args}"
 -> (0..10).map(|f| rsx!("asd")),  // <--- notice the comma - must be a complete expr
 */
-#[derive(PartialEq, Eq)]
+#[derive(PartialEq, Eq, Clone, Debug, Hash)]
 pub enum BodyNode {
     Element(Element),
     Component(Component),
-    Text(LitStr),
+    Text(IfmtInput),
     RawExpr(Expr),
 }
 
@@ -33,7 +33,7 @@ impl BodyNode {
         match self {
             BodyNode::Element(el) => el.name.span(),
             BodyNode::Component(component) => component.name.span(),
-            BodyNode::Text(text) => text.span(),
+            BodyNode::Text(text) => text.source.span(),
             BodyNode::RawExpr(exp) => exp.span(),
         }
     }
@@ -98,7 +98,7 @@ impl ToTokens for BodyNode {
             BodyNode::Element(el) => el.to_tokens(tokens),
             BodyNode::Component(comp) => comp.to_tokens(tokens),
             BodyNode::Text(txt) => tokens.append_all(quote! {
-                __cx.text(format_args_f!(#txt))
+                __cx.text(#txt)
             }),
             BodyNode::RawExpr(exp) => tokens.append_all(quote! {
                  __cx.fragment_from_iter(#exp)