chore: move gamma components into dedicated directories (#3243)

## Description

Moves gamma components (`SplitView`, new `Stack`) into dedicated
directories in `src/components/gamma`.

Closes
software-mansion/react-native-screens-labs#445.

## Changes

- move gamma components (`SplitView`, new `Stack`) into dedicated
directories in `src/components/gamma`
- update imports

## Test code and steps to reproduce

Run `TestSplitView`, `TestScreenStack` and verify that the components
work correctly.

## Checklist

- [x] Included code example that can be used to test this change
- [x] Ensured that CI passes

Author: kligarski

src/components/gamma/SplitViewHost.tsx renamed to src/components/gamma/split-view/SplitViewHost.tsx

@@ -1,6 +1,6 @@
 import React from 'react';
 import { StyleSheet } from 'react-native';
-import SplitViewHostNativeComponent from '../../fabric/gamma/SplitViewHostNativeComponent';
+import SplitViewHostNativeComponent from '../../../fabric/gamma/SplitViewHostNativeComponent';
 import type {
   SplitViewDisplayMode,
   SplitViewHostProps,

src/components/gamma/SplitViewHost.types.ts renamed to src/components/gamma/split-view/SplitViewHost.types.ts

@@ -1,6 +1,6 @@
 import React from 'react';
 import { StyleSheet } from 'react-native';
-import SplitViewScreenNativeComponent from '../../fabric/gamma/SplitViewScreenNativeComponent';
+import SplitViewScreenNativeComponent from '../../../fabric/gamma/SplitViewScreenNativeComponent';
 import { SplitViewScreenProps } from './SplitViewScreen.types';
 
 /**

src/components/gamma/SplitViewHost.web.tsx renamed to src/components/gamma/split-view/SplitViewHost.web.tsx

@@ -1,6 +1,6 @@
 import React from 'react';
 import { StyleSheet } from 'react-native';
-import ScreenStackHostNativeComponent from '../../fabric/gamma/ScreenStackHostNativeComponent';
+import ScreenStackHostNativeComponent from '../../../fabric/gamma/ScreenStackHostNativeComponent';
 import type { ScreenStackHostProps } from './ScreenStackHost.types';
 
 /**

src/components/gamma/SplitViewScreen.tsx renamed to src/components/gamma/split-view/SplitViewScreen.tsx

@@ -1,6 +1,6 @@
 import React from 'react';
 import { StyleSheet } from 'react-native';
-import StackScreenNativeComponent from '../../fabric/gamma/StackScreenNativeComponent';
+import StackScreenNativeComponent from '../../../fabric/gamma/StackScreenNativeComponent';
 import type { NativeSyntheticEvent } from 'react-native';
 import { StackScreenProps } from './StackScreen.types';