Document property/item creation batching

Repro:

Create directory structure and empty files like so:
```
A\1.stub
B\2.stub
B\3.stub
```

and run targets file in the same dir as A and B:

```xml

<_StubFiles Include="$(MSBuildThisFileDirectory)**\*.stub"/>

<_StubDirs Include="@(_StubFiles->'%(RecursiveDir)')"/>




<_ComponentDir>%(_StubDirs.Identity)
<_ComponentName>$(_ComponentDir.TrimEnd('\'))

```

Actual output:
```
>> A\ 'B\' 'B'
>> B\ 'B\' 'B'
```

Expected output:
```
>> A\ 'A\' 'A'
>> B\ 'B\' 'B'
```