Initial `width` and `height` are inaccurate when manually setting `.defaultSize` on `RCTMainWindow`

[billyjacoby]

Description

When setting a custom height and/or width on the RCTMainWindow, the values reported by useWindowDimension are incorrect until the window is either moved or resized.

Steps to reproduce

1. Init a new project via the instructions in the readme
2. Change the default window size by setting .defaultSize(.init(width: 2000, height: 180)) on RCTMainWindow
3. Log the results of useWindowDimensions in the app file, and note the difference between the initially logged value and window size

React Native Version

0.73.4

Affected Platforms

Other (please specify)

Output of npx react-native info

System:
  OS: macOS 14.2.1
  CPU: (12) arm64 Apple M2 Max
  Memory: 196.42 MB / 32.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 20.5.0
    path: ~/.nvm/versions/node/v20.5.0/bin/node
  Yarn:
    version: 4.1.0
    path: ~/.nvm/versions/node/v20.5.0/bin/yarn
  npm:
    version: 9.8.0
    path: ~/.nvm/versions/node/v20.5.0/bin/npm
  Watchman:
    version: 2024.01.15.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.15.2
    path: /opt/homebrew/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 23.2
      - iOS 17.2
      - macOS 14.2
      - tvOS 17.2
      - visionOS 1.0
      - watchOS 10.2
  Android SDK: Not Found
IDEs:
  Android Studio: 2023.1 AI-231.9392.1.2311.11330709
  Xcode:
    version: 15.2/15C500b
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 17.0.10
    path: /usr/bin/javac
  Ruby:
    version: 2.6.10
    path: /usr/bin/ruby
npmPackages:
  "@react-native-community/cli": Not Found
  react:
    installed: 18.2.0
    wanted: 18.2.0
  react-native:
    installed: 0.73.4
    wanted: 0.73.4
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: false
iOS:
  hermesEnabled: true
  newArchEnabled: false

### Stacktrace or Logs

```text
LOG  🪵 | height: 720
 LOG  🪵 | width: 1280

Reproducer

https://github.com/billyjacoby/callstack-visionos-repro/tree/window-size

Screenshots and Videos

I have very limited experience with the native library portion of React Native, but if someone wants to point me in the right direction I'm happy to try and fix this issue.

I assume the initial size just isn't being sent to the RN side of things for some reason.