[WASM] Listview header and footer are not implemented

[soriyathach]

Current behavior

The listview is not displayed at all if a header or footer is specified on a listview.

Expected behavior

The header, footer and listview content should be displayed.

How to reproduce it (as minimally and precisely as possible)

Seems like nothing is implemented on ListViewBase for wasm:
https://github.com/unoplatform/uno/blob/8dcc6f2d3aa5d57fd3ee96efe5fe73855a45a0da/src/Uno.UI/UI/Xaml/Controls/ListViewBase/ListViewBase.netstd.cs

Environment

Nuget Package:

Package Version(s):
UNO.UI 1.46.196-dev.2440

Affected platform(s):

• iOS
• Android
• WebAssembly
• WebAssembly renderers for Xamarin.Forms
• Windows
• Build tasks
• Solution Templates

Visual Studio:

• 2017 (version: )
• 2019 (version: 16.2.0)
• for Mac (version: )

Relevant plugins:

• Resharper (version: )

Anything else we need to know?