Add Count and Length properties to [PSCustomobject] (#5745)

Related #3671
•Add Count and Length properties to [PSCustomobject].
 Now following returns 1:
 ([pscustomobject] @{ foo = 'bar' }).Count
 ([pscustomobject] @{ foo = 'bar' }).Length
•Add tests

src/System.Management.Automation/engine/runtime/Binding/Binders.cs

@@ -5690,6 +5690,11 @@ namespace System.Management.Automation.Language
                 return memberInfo.Value;
             }
 
+            if (string.Equals(member, "Length", StringComparison.OrdinalIgnoreCase) || string.Equals(member, "Count", StringComparison.OrdinalIgnoreCase))
+            {
+                return 1;
+            }
+
             if (context != null && context.IsStrictVersion(2))
             {
                 // If the member is undefined and we're in strict mode, throw an exception...

test/powershell/engine/ETS/Adapter.Tests.ps1

@@ -112,6 +112,33 @@ Describe "Adapter Tests" -tags "CI" {
             Remove-TypeData TestCodeMethodInvokationWithVoidReturn
         }
     }
+
+    It "Count and length property works for singletons" {
+        # Return magic Count and Length property if it absent.
+        $x = 5
+        $x.Count | Should Be 1
+        $x.Length | Should Be 1
+
+        $null.Count | Should Be 0
+        $null.Length | Should Be 0
+
+        (10).Count | Should Be 1
+        (10).Length | Should Be 1
+
+        ("a").Count | Should Be 1
+        # The Length property exists for strings, so we skip the test in the context.
+        # ("a").Length | Should Be 1
+
+        ([psobject] @{ foo = 'bar' }).Count | Should Be 1
+        ([psobject] @{ foo = 'bar' }).Length | Should Be 1
+
+        ([pscustomobject] @{ foo = 'bar' }).Count | Should Be 1
+        ([pscustomobject] @{ foo = 'bar' }).Length | Should Be 1
+
+        # Return real Count and Length property if it present.
+        ([pscustomobject] @{ foo = 'bar'; count = 5 }).Count | Should Be 5
+        ([pscustomobject] @{ foo = 'bar'; length = 5 }).Length | Should Be 5
+    }
 }
 
 Describe "Adapter XML Tests" -tags "CI" {