Caret behavior by long tap in cupertino textfield (#913)

## Proposed Changes

Added native behavior for long tap and drag in Cupertino text field.
Unlike Android, long tap and drag gesture doesn't enter selection mode,
It just moves the cursor.

## Testing

Test: Open test app, go Components -> Text fields -> Almost fullscreen,
tap on the textfield to focus it, then try to long tap in somewhere else
and drag.

## Issues Fixed

-
https://youtrack.jetbrains.com/issue/COMPOSE-449/iOS-caret-movement-by-long-tap-in-textfields
-
https://youtrack.jetbrains.com/issue/COMPOSE-448/iOS-separate-long-tap-logic-and-drag-selection-logic-in-textfields
(it is related to the issue above)

## Google CLA
You need to sign the Google Contributor’s License Agreement at
https://cla.developers.google.com/.
This is needed since we synchronise most of the code with Google’s AOSP
repository. Signing this agreement allows us to synchronise code from
your Pull Requests as well.

---------

Co-authored-by: Igor Demin <[email protected]>
Co-authored-by: Ivan Matkov <[email protected]>
Co-authored-by: Elijah Semyonov <[email protected]>
Co-authored-by: dima.avdeev <[email protected]>
Co-authored-by: Alexander Maryanovsky <[email protected]>
Co-authored-by: Oleksandr Karpovich <[email protected]>
Co-authored-by: Nikolai Rykunov <[email protected]>
Co-authored-by: Konstantin <[email protected]>
Co-authored-by: Farouk Abichou <[email protected]>
Co-authored-by: Alexander Zhirkevich <[email protected]>
Co-authored-by: Jake Wharton <[email protected]>
Co-authored-by: Sebastian <[email protected]>
Co-authored-by: Igor Demin <[email protected]>
Co-authored-by: Oleksandr Karpovich <[email protected]>
Co-authored-by: sanao <[email protected]>

compose/foundation/foundation/src/skikoMain/kotlin/androidx/compose/foundation/text/CupertinoTextFieldPointerModifier.skiko.kt

@@ -48,7 +48,7 @@ internal fun Modifier.cupertinoTextFieldPointer(
     offsetMapping: OffsetMapping
 ): Modifier = if (enabled) {
     if (isInTouchMode) {
-        val selectionModifier = getSelectionModifier(manager)
+        val longPressHandlerModifier = getLongPressHandlerModifier(state, offsetMapping)
         val tapHandlerModifier = getTapHandlerModifier(
             interactionSource,
             state,
@@ -59,7 +59,7 @@ internal fun Modifier.cupertinoTextFieldPointer(
         )
         this
             .then(tapHandlerModifier)
-            .then(selectionModifier)
+            .then(longPressHandlerModifier)
             .pointerHoverIcon(textPointerIcon)
     } else {
         this
@@ -142,19 +142,70 @@ private fun getTapHandlerModifier(
     }
 }
 
+/**
+ * Returns a modifier which allows to precisely move the caret in the text by drag gesture after long press
+ *
+ * @param state The state of the text field.
+ * @param offsetMapping The offset mapping of the text field.
+ * @return A modifier that handles long press and drag gestures.
+ */
 @Composable
-private fun getSelectionModifier(manager: TextFieldSelectionManager): Modifier {
-    val currentManager by rememberUpdatedState(manager)
+private fun getLongPressHandlerModifier(
+    state: TextFieldState,
+    offsetMapping: OffsetMapping
+): Modifier {
+    val currentState by rememberUpdatedState(state)
+    val currentOffsetMapping by rememberUpdatedState(offsetMapping)
+
     return Modifier.pointerInput(Unit) {
+        val longTapActionsObserver =
+            object : TextDragObserver {
+                var dragTotalDistance = Offset.Zero
+                var dragBeginOffset = Offset.Zero
+
+                override fun onStart(startPoint: Offset) {
+                    currentState.layoutResult?.let { layoutResult ->
+                        TextFieldDelegate.setCursorOffset(
+                            startPoint,
+                            layoutResult,
+                            currentState.processor,
+                            currentOffsetMapping,
+                            currentState.onValueChange
+                        )
+                        dragBeginOffset = startPoint
+                    }
+                    dragTotalDistance = Offset.Zero
+                }
+
+                override fun onDrag(delta: Offset) {
+                    dragTotalDistance += delta
+                    currentState.layoutResult?.let { layoutResult ->
+                        val currentDragPosition = dragBeginOffset + dragTotalDistance
+                        TextFieldDelegate.setCursorOffset(
+                            currentDragPosition,
+                            layoutResult,
+                            currentState.processor,
+                            currentOffsetMapping,
+                            currentState.onValueChange
+                        )
+                    }
+                }
+
+                // Unnecessary here
+                override fun onDown(point: Offset) {}
+
+                override fun onUp() {}
+
+                override fun onStop() {}
+
+                override fun onCancel() {}
+            }
+
         detectDragGesturesAfterLongPress(
-            onDragStart = {
-                currentManager.touchSelectionObserver.onStart(
-                    startPoint = it
-                )
-            },
-            onDrag = { _, delta -> currentManager.touchSelectionObserver.onDrag(delta = delta) },
-            onDragCancel = { currentManager.touchSelectionObserver.onCancel() },
-            onDragEnd = { currentManager.touchSelectionObserver.onStop() }
+            onDragStart = { longTapActionsObserver.onStart(it) },
+            onDrag = { _, delta -> longTapActionsObserver.onDrag(delta = delta) },
+            onDragCancel = { longTapActionsObserver.onCancel() },
+            onDragEnd = { longTapActionsObserver.onStop() }
         )
     }
 }