Fix broken examples and code highlighting in ViewTransition and addTransitionType

The fixed example in "two <ViewTransition name=%s> components" still
passes item={item} while Item reads {id}, so every item is named
"item-undefined" and triggers the same error. The first addTransitionType
example has a syntax error ({action)) and a fence without a language, so
its CodeSteps never render.

Line highlights written as [3, 5] / [3] / [11] are ignored by
getHighlightLines, which only reads {...}; switch them to braces and
update ranges that no longer match the code.

Also use checked instead of value on the "Fast" checkbox, move key to
the outer element in the wrapper snippet, drop the nonexistent `layout`
prop from addTransitionType, and remove a "sidebar" reference from the
Activity example, which only has a counter.

Author: BlackHatMan

src/content/reference/react/ViewTransition.md

@@ -442,7 +442,7 @@ button:hover {
 
 If there's a `<div>` above `<ViewTransition>`, no exit/enter animations trigger:
 
-```js [3, 5]
+```js {3,7}
 function Item() {
   return (
     <div> {/* 🚩<div> above <ViewTransition> breaks exit/enter */}
@@ -473,7 +473,7 @@ If you want to animate a component in and out while preserving its state, or pre
 
 ```
 
-In this example, `Counter` has a counter with internal state. Try incrementing the counter, hiding it, then showing it again. The counter's value is preserved while the sidebar animates in and out:
+In this example, `Counter` has a counter with internal state. Try incrementing the counter, hiding it, then showing it again. The counter's value is preserved while `Counter` animates in and out:
 
 <Sandpack>
 
@@ -574,7 +574,7 @@ function Counter() {
 
 </Sandpack>
 
-Without `<Activity>`, the counter would reset to `0` every time the sidebar reappears.
+Without `<Activity>`, the counter would reset to `0` every time it reappears.
 
 ---
 
@@ -1235,8 +1235,8 @@ button:hover {
 
 This means you might want to avoid wrapper elements in lists where you want to allow the Component to control its own reorder animation:
 
-```
-items.map(item => <div><Component key={item.id} item={item} /></div>)
+```js
+items.map(item => <div key={item.id}><Component item={item} /></div>)
 ```
 
 The above rule also applies if one of the items updates to resize, which then causes the siblings to resize, it'll also animate its sibling `<ViewTransition>` but only if they're immediate siblings.
@@ -2630,7 +2630,7 @@ export default function Component() {
   return (
     <>
       <div>
-        Fast: <input type="checkbox" onChange={() => {setIsFast(f => !f)}} value={isFast}></input>
+        Fast: <input type="checkbox" onChange={() => {setIsFast(f => !f)}} checked={isFast}></input>
       </div><br />
       <button
         onClick={() => {
@@ -2783,7 +2783,7 @@ If a `startTransition` is started from the legacy popstate event, such as during
 
 `<ViewTransition>` only activates if it is placed before any DOM node:
 
-```js [3, 5]
+```js {3,5}
 function Component() {
   return (
     <div>
@@ -2795,7 +2795,7 @@ function Component() {
 
 To fix, ensure that the `<ViewTransition>` comes before any other DOM nodes:
 
-```js [3, 5]
+```js {3,5}
 function Component() {
   return (
     <ViewTransition>
@@ -2809,7 +2809,7 @@ function Component() {
 
 This error occurs when two `<ViewTransition>` components with the same `name` are mounted at the same time:
 
-```js [3]
+```js {3}
 function Item() {
   // 🚩 All items will get the same "name".
   return <ViewTransition name="item">...</ViewTransition>;
@@ -2848,7 +2848,7 @@ The existing `<ViewTransition name=%s>` duplicate has this stack trace.
 
 To fix, ensure that there's only one `<ViewTransition>` with the same name mounted at a time in the entire app by ensuring the `name` is unique, or adding an `id` to the name:
 
-```js [3]
+```js {3}
 function Item({id}) {
   // ✅ All items will get a unique name.
   return <ViewTransition name={`item-${id}`}>...</ViewTransition>;
@@ -2858,7 +2858,7 @@ function ItemList({items}) {
   return (
     <>
       {items.map((item) => (
-        <Item key={item.id} item={item} />
+        <Item key={item.id} id={item.id} />
       ))}
     </>
   );

src/content/reference/react/addTransitionType.md

@@ -45,10 +45,10 @@ startTransition(() => {
 
 Call `addTransitionType` inside of `startTransition` to indicate the cause of a transition:
 
-``` [[1, 6, "addTransitionType"], [2, 5, "startTransition", [3, 6, "'submit-click'"]]
+```js [[1, 6, "addTransitionType"], [2, 5, "startTransition"], [3, 6, "'submit-click'"]]
 import { startTransition, addTransitionType } from 'react';
 
-function Submit({action) {
+function Submit({action}) {
   function handleClick() {
     startTransition(() => {
       addTransitionType('submit-click');
@@ -78,7 +78,7 @@ When a [`ViewTransition`](/reference/react/ViewTransition) activates from a tran
 
 This allows you to customize different animations based on CSS scopes:
 
-```js [11]
+```js {10}
 function Component() {
   return (
     <ViewTransition>
@@ -127,7 +127,7 @@ startTransition(() => {
 
 If multiple types match, then they're joined together. If no types match then the special "default" entry is used instead. If any type has the value "none" then that wins and the ViewTransition is disabled (not assigned a name).
 
-These can be combined with enter/exit/update/layout/share props to match based on kind of trigger and Transition Type.
+These can be combined with enter/exit/update/share props to match based on kind of trigger and Transition Type.
 
 ```js
 <ViewTransition enter={{