Repository: flutter
Issue: [Impeller] elevation lacks any shadow at top of the material widget
Labels: P2,e: impeller,team-engine,triaged-engine

## description

When using the elevation parameter on the Material widget there is zero shadow at the top of the widget.  Skia would render a hairline shadow around the whole widget.  It is very tiny but I worry that in particular cases it can cause accessibility problems where there is no visual delimiter between widgets (vision impairment, dyslexia, etc).

spawned from https://github.com/flutter/flutter/issues/149474
seen at 3dd40156afb6f878597d7018ea769b752ca5b115

## observed result

The top of the widget has no shadow.

## expected result

I expect a hairline shadow at the top of the widget.

## frame capture

[column3materials.gputrace.zip](https://github.com/user-attachments/files/15594418/column3materials.gputrace.zip)

## image

Notice how skia has a hairline shadow at the top.

![ezgif-7-ad6aaa73f8](https://github.com/flutter/flutter/assets/30870216/ca57f27c-23e0-45ac-9044-9193a25af44b)

## reproduction code

```dart
import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key});
  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: const Text("Impeller"),
      ),
      body: Center(
        child: IntrinsicWidth(
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.stretch,
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Material(
                color: Theme.of(context).colorScheme.onSecondary,
                elevation: 5,
                borderRadius: const BorderRadius.only(
                  topLeft: Radius.circular(25),
                  topRight: Radius.circular(25),
                ),
                child: const Padding(
                  padding: EdgeInsets.all(16.0),
                  child: Text("Top"),
                ),
              ),
              Material(
                color: Theme.of(context).colorScheme.onSecondary,
                elevation: 5,
                // borderRadius: BorderRadius.circular(25),
                child: const Padding(
                  padding: EdgeInsets.all(16.0),
                  child: Text("Middle"),
                ),
              ),
              Material(
                color: Theme.of(context).colorScheme.onSecondary,
                elevation: 5,
                borderRadius: const BorderRadius.only(
                  topLeft: Radius.zero,
                  bottomLeft: Radius.circular(25),
                  topRight: Radius.zero,
                  bottomRight: Radius.circular(25),
                ),
                child: const Padding(
                  padding: EdgeInsets.all(16.0),
                  child: Text("Bottom"),
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}


```