[Docs] Restructure SideBar (#4365)

## Description

This PR:

- Extracts `GestureHandlerRootView` and `GestureDetector` out of
Fundamentals into a new "Core Components" section
- Moves State manager from Fundamentals to Gestures
- Renames "Quick start" to "Your first gesture-driven animation" and
moves it under Fundamentals
- Renames the Gestures category to "Gestures API"
- Fixes page ordering (sidebar_position) across Components/Guides
- Adds redirects for all removed/moved pages (gesture-detectors,
root-view, quickstart, state manager)
- Updates mapLegacyUrl.js so  /quickstart URLs resolve correctly
- Fixes ~30 internal doc links broken by the moves above

## Test plan

- `yarn build`
- Read docs 🤓

Author: m-bert

packages/docs-gesture-handler/docs/components/_category_.json

@@ -1,6 +1,6 @@
 {
   "label": "Components",
-  "position": 4,
+  "position": 6,
   "link": {
     "type": "generated-index"
   }

packages/docs-gesture-handler/docs/components/buttons.mdx

@@ -2,6 +2,7 @@
 id: buttons
 title: Buttons
 sidebar_label: Buttons
+sidebar_position: 6
 ---
 
 import useBaseUrl from '@docusaurus/useBaseUrl';

packages/docs-gesture-handler/docs/components/pressable.mdx

@@ -2,6 +2,7 @@
 id: pressable
 title: Pressable
 sidebar_label: Pressable
+sidebar_position: 2
 ---
 
 import useBaseUrl from '@docusaurus/useBaseUrl';
@@ -17,7 +18,7 @@ This component is a drop-in replacement for the `Pressable` component.
 
 `Pressable` is a component that can detect various stages of tap, press, and hover interactions on any of its children.
 
-To use `Pressable`, ensure that your app is wrapped in [`GestureHandlerRootView`](/docs/fundamentals/root-view) and import it as follows:
+To use `Pressable`, ensure that your app is wrapped in [`GestureHandlerRootView`](/docs/core-components/root-view) and import it as follows:
 
 ```ts
 import { Pressable } from 'react-native-gesture-handler';

packages/docs-gesture-handler/docs/components/reanimated-drawer-layout.mdx

@@ -2,6 +2,7 @@
 id: reanimated-drawer-layout
 title: Reanimated Drawer Layout
 sidebar_label: Reanimated Drawer Layout
+sidebar_position: 4
 ---
 
 import useBaseUrl from '@docusaurus/useBaseUrl';
@@ -12,7 +13,7 @@ import MouseButtonProp from '../gestures/\_shared/mouse-button.mdx';
 This component acts as a cross-platform replacement for React Native's [`DrawerLayoutAndroid`](http://reactnative.dev/docs/drawerlayoutandroid.html) component, written using [Reanimated](https://docs.swmansion.com/react-native-reanimated/docs/fundamentals/getting-started). For detailed information on standard parameters, please refer to the [React Native documentation](http://reactnative.dev/docs/drawerlayoutandroid.html).
 :::
 
-To use `ReanimatedDrawerLayout`, first ensure that Reanimated is installed and that your app is wrapped in [`GestureHandlerRootView`](/docs/fundamentals/root-view). You can then import it as follows:
+To use `ReanimatedDrawerLayout`, first ensure that Reanimated is installed and that your app is wrapped in [`GestureHandlerRootView`](/docs/core-components/root-view). You can then import it as follows:
 
 ```ts
 import ReanimatedDrawerLayout from 'react-native-gesture-handler/ReanimatedDrawerLayout';

packages/docs-gesture-handler/docs/components/reanimated_swipeable.mdx

@@ -2,6 +2,7 @@
 id: reanimated_swipeable
 title: Reanimated Swipeable
 sidebar_label: Reanimated Swipeable
+sidebar_position: 3
 ---
 
 import useBaseUrl from '@docusaurus/useBaseUrl';

packages/docs-gesture-handler/docs/components/touchable.mdx

@@ -2,6 +2,7 @@
 id: touchable
 title: Touchable
 sidebar_label: Touchable
+sidebar_position: 1
 ---
 
 :::note

packages/docs-gesture-handler/docs/components/touchables.md

@@ -2,6 +2,7 @@
 id: legacy-touchables
 title: Legacy Touchables
 sidebar_label: Legacy Touchables
+sidebar_position: 7
 ---
 
 :::warning

packages/docs-gesture-handler/docs/components/wrapped-components.mdx

@@ -2,6 +2,7 @@
 id: wrapped-components
 title: Wrapped Components
 sidebar_label: Wrapped Components
+sidebar_position: 5
 ---
 
 Some components come with a [`Native`](/docs/gestures/use-native-gesture) gesture pre-applied. This allows them to participate in the gesture recognition process. Have a look at the example below.

packages/docs-gesture-handler/docs/composition/_category_.json

@@ -1,6 +1,6 @@
 {
   "label": "Gesture composition & interactions",
-  "position": 3,
+  "position": 5,
   "link": {
     "type": "generated-index"
   }

packages/docs-gesture-handler/docs/composition/overview.mdx

@@ -7,7 +7,7 @@ sidebar_position: 0
 
 Gesture Handler simplifies gesture interactions through dedicated composition hooks and relation properties. To choose the right approach, simply ask: are all the gestures attached to the same component?
 
-- If **yes** — use [composition hooks](#composition-hooks). These allow you to bundle multiple gestures — including previously composed ones — into a single object for a [`GestureDetector`](/docs/fundamentals/gesture-detectors).
+- If **yes** — use [composition hooks](#composition-hooks). These allow you to bundle multiple gestures — including previously composed ones — into a single object for a [`GestureDetector`](/docs/core-components/gesture-detectors).
 - If **no** — use [relation properties](#cross-component-interactions) to manually define how gestures interact. Since these properties also support composed gestures, you can mix both methods for more complex layouts.
 
 ## Composition hooks