Fix content rect calculation in SelectionManager (#1270)

## Proposed Changes

**Cherry-picked from androidx**

Fix a typo in `SelectionManager.getContentRect()` that results in an
invalid rect being calculated, causing text toolbar to not show under
certain conditions.

Fixes: b/332782845
Test: manual
Change-Id: I153b99f4146d870182af2898d9a675ed6ffa15e4

## Testing

Test: Open test app, go Components -> Selection, try to select text in
selection container

## Issues Fixed

Fixes: appearing of editing menu in selection container in wrong
position

https://youtrack.jetbrains.com/issue/COMPOSE-1190/iOS-Selection-Container-cant-show-options-menu
JetBrains/compose-multiplatform#4322
b/332782845 in Google

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Co-authored-by: Albert Chang <mxalbert1996@gmail.com>

compose/foundation/foundation/src/commonMain/kotlin/androidx/compose/foundation/text/selection/SelectionManager.kt

@@ -591,7 +591,7 @@ internal class SelectionManager(private val selectionRegistrar: SelectionRegistr
         if (visibleRect.width < 0 || visibleRect.height < 0) return null
 
         val rootRect = visibleRect.translate(containerCoordinates.positionInRoot())
-        return rootRect.copy(bottom = visibleRect.bottom + HandleHeight.value * 4)
+        return rootRect.copy(bottom = rootRect.bottom + HandleHeight.value * 4)
     }
 
     // This is for PressGestureDetector to cancel the selection.