Fix PowerShell class to support deriving from an abstract class with abstract properties (#21331)

test/powershell/Language/Classes/scripting.Classes.inheritance.tests.ps1

@@ -628,3 +628,47 @@ class Derived : Base
         $sb.Invoke() | Should -Be 200
     }
 }
+
+Describe 'Base type has abstract properties' -Tags "CI" {
+    It 'can derive from `FileSystemInfo`' {
+        ## FileSystemInfo has 3 abstract members that a derived type needs to implement
+        ##  - public abstract bool Exists { get; }
+        ##  - public abstract string Name { get; }
+        ##  - public abstract void Delete ();
+
+        class myFileSystemInfo : System.IO.FileSystemInfo
+        {
+            [string] $Name
+            [bool] $Exists
+
+            myFileSystemInfo([string]$path)
+            {
+                # ctor
+                $this.Name = $path
+                $this.Exists = $true
+            }
+
+            [void] Delete()
+            {
+            }
+        }
+
+        $myFile = [myFileSystemInfo]::new('Hello')
+        $myFile.Name | Should -Be 'Hello'
+        $myFile.Exists | Should -BeTrue
+    }
+
+    It 'deriving from `FileSystemInfo` will fail when the abstract property `Exists` is not implemented' {
+        $script = [scriptblock]::Create('class WillFail : System.IO.FileSystemInfo { [string] $Name }')
+        $failure = $null
+        try {
+            & $script
+        } catch {
+            $failure = $_
+        }
+
+        $failure | Should -Not -BeNullOrEmpty
+        $failure.FullyQualifiedErrorId | Should -BeExactly "TypeCreationError"
+        $failure.Exception.Message | Should -BeLike "*'get_Exists'*"
+    }
+}