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/autofmt/src/buffer.rs

@@ -3,7 +3,7 @@ use std::{
     fmt::{Result, Write},
 };
 
-use dioxus_rsx::{BodyNode, ElementAttr, ElementAttrNamed};
+use dioxus_rsx::{BodyNode, ElementAttr, ElementAttrNamed, IfmtInput};
 use proc_macro2::{LineColumn, Span};
 use syn::{spanned::Spanned, Expr};
 
@@ -72,8 +72,8 @@ impl Buffer {
         }
     }
 
-    pub fn write_text(&mut self, text: &syn::LitStr) -> Result {
-        write!(self.buf, "\"{}\"", text.value())
+    pub fn write_text(&mut self, text: &IfmtInput) -> Result {
+        write!(self.buf, "\"{}\"", text.source.as_ref().unwrap().value())
     }
 
     pub fn consume(self) -> Option<String> {
@@ -155,13 +155,13 @@ impl Buffer {
 
             total += match &attr.attr {
                 ElementAttr::AttrText { value, name } => {
-                    value.value().len() + name.span().line_length() + 3
+                    value.source.as_ref().unwrap().value().len() + name.span().line_length() + 3
                 }
                 ElementAttr::AttrExpression { name, value } => {
                     value.span().line_length() + name.span().line_length() + 3
                 }
                 ElementAttr::CustomAttrText { value, name } => {
-                    value.value().len() + name.value().len() + 3
+                    value.source.as_ref().unwrap().value().len() + name.value().len() + 3
                 }
                 ElementAttr::CustomAttrExpression { name, value } => {
                     name.value().len() + value.span().line_length() + 3