refactor!: use the KeyboardObserver package (#607)

This removes the internal `KeyboardObserver` and replaces it with
https://github.com/square/swift-keyboard-observer. This also removes
`SetupKeyboardObserverOnAppStartup.m` since we no longer support
CocoaPods.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: johnnewman-square

.gitignore

@@ -37,9 +37,11 @@ playground.xcworkspace
 # Add this line if you want to avoid checking in source code from Swift Package Manager dependencies.
 # Packages/
 # Package.pins
-# Package.resolved
 .build/
 
+# Resolved dependencies are managed by Tuist in Development/Tuist/Package.resolved.
+Package.resolved
+
 # Carthage
 #
 # Add this line if you want to avoid checking in source code from Carthage dependencies.

CHANGELOG.md

@@ -8,6 +8,8 @@
 
 ### Changed
 
+- Replaced the internal `KeyboardObserver` with https://github.com/square/swift-keyboard-observer.
+
 ### Misc
 
 ### Internal