Introduce methods for computing the baseline location of a RenderBox …

…without affecting the current layout (flutter#144655)

Extracted from flutter#138369

Introduces `RenderBox.{compute,get}DryBaseline` for computing the baseline location in `RenderBox.computeDryLayout`.

packages/flutter/lib/src/material/input_decorator.dart

@@ -1316,7 +1316,10 @@ class _RenderDecoration extends RenderBox with SlottedContainerRenderObjectMixin
 
   @override
   double computeDistanceToActualBaseline(TextBaseline baseline) {
-    return _boxParentData(input!).offset.dy + (input?.computeDistanceToActualBaseline(baseline) ?? 0.0);
+    final RenderBox? input = this.input;
+    return input == null
+      ? 0.0
+      : _boxParentData(input).offset.dy + (input.computeDistanceToActualBaseline(baseline) ?? 0.0);
   }
 
   // Records where the label was painted.

packages/flutter/lib/src/material/list_tile.dart

@@ -1249,10 +1249,12 @@ class _RenderListTile extends RenderBox with SlottedContainerRenderObjectMixin<_
   }
 
   @override
-  double computeDistanceToActualBaseline(TextBaseline baseline) {
+  double? computeDistanceToActualBaseline(TextBaseline baseline) {
     assert(title != null);
     final BoxParentData parentData = title!.parentData! as BoxParentData;
-    return parentData.offset.dy + title!.getDistanceToActualBaseline(baseline)!;
+    final BaselineOffset offset = BaselineOffset(title!.getDistanceToActualBaseline(baseline))
+                                + parentData.offset.dy;
+    return offset.offset;
   }
 
   static double? _boxBaseline(RenderBox box, TextBaseline baseline) {

packages/flutter/lib/src/material/toggle_buttons.dart

@@ -1175,11 +1175,13 @@ class _SelectToggleButtonRenderObject extends RenderShiftedBox {
   }
 
   @override
-  double computeDistanceToActualBaseline(TextBaseline baseline) {
+  double? computeDistanceToActualBaseline(TextBaseline baseline) {
     // The baseline of this widget is the baseline of its child
-    return direction == Axis.horizontal
-      ? child!.computeDistanceToActualBaseline(baseline)! + borderSide.width
-      : child!.computeDistanceToActualBaseline(baseline)! + leadingBorderSide.width;
+    final BaselineOffset childOffset = BaselineOffset(child?.computeDistanceToActualBaseline(baseline));
+    return switch (direction) {
+      Axis.horizontal => childOffset + borderSide.width,
+      Axis.vertical => childOffset + leadingBorderSide.width,
+    }.offset;
   }
 
   @override