Disable encoding on separate thread for iOS (#907)

## Proposed Changes

Using Skia context in multiple threads simultaneously leads to
occasional unreproducable crashes on users' side.
Roll back experimental #896. Disable the path for encoding rendering
commands on a separate thread until the scenario is resolved and
underlying issue is fixed.

## Testing

Test: N/A

## Issues Fixed

Fixes: JetBrains/compose-multiplatform#3862

compose/ui/ui/src/uikitMain/kotlin/androidx/compose/ui/window/MetalRedrawer.kt

@@ -381,7 +381,11 @@ internal class MetalRedrawer(
                 isForcedToPresentWithTransactionEveryFrame || interopTransaction.isNotEmpty()
             metalLayer.presentsWithTransaction = presentsWithTransaction
 
-            val mustEncodeAndPresentOnMainThread = presentsWithTransaction || waitUntilCompletion
+            // TODO: encoding on separate thread requires investigation for reported crashes
+            //  https://github.com/JetBrains/compose-multiplatform/issues/3862
+            //  https://youtrack.jetbrains.com/issue/COMPOSE-608/iOS-reproduce-and-investigate-parallel-rendering-encoding-crash
+            // val mustEncodeAndPresentOnMainThread = presentsWithTransaction || waitUntilCompletion
+            val mustEncodeAndPresentOnMainThread = true
 
             val encodeAndPresentBlock = {
                 surface.canvas.drawPicture(picture)