Trim whitespace when parsing `<TraverseFiles>` contents?

For https://github.com/Tsukisoft/direct-storage-rs/pull/5

We had a list of the form:

```xml

$(PkgMicrosoft_Direct3D_DirectStorage)\native\include\dstorage.h;
$(PkgMicrosoft_Direct3D_DirectStorage)\native\include\dstorageerr.h

```

But no constants from `dstorageerr.h` were parsed. Swapping the filenames makes it so that `#define`s from `dstorage.h` are lost, but defines from `dstorageerr.h` are parsed.

I believe the raw string it's parsing here is: `dstorage.h;\ndstorageerr.h\n`, splitting this on `;` causes the last filename to never match. Perhaps a `string item = items[i].Trim();` is missing here to make multiline filename strings work more naturally?

https://github.com/microsoft/win32metadata/blob/3d2ba1e501e46f078e4b4670a52ed68890870f8a/sources/GeneratorSdk/MetadataTasks/ScrapeHeaders.cs#L476-L488

After all, when merging this into one line:

```xml
$(PkgMicrosoft_Direct3D_DirectStorage)\native\include\dstorage.h;$(PkgMicrosoft_Direct3D_DirectStorage)\native\include\dstorageerr.h
```

Both files were finally parsed correctly.

Start with sources/GeneratorSdk/MetadataTasks/ScrapeHeaders.cs lines 476-488 and reproduce the multiline input using the two DirectStorage headers shown in the issue. Verify that parsing the newline-separated entries recognizes both headers and that the corresponding defines are processed.

Written by the indexing model from the issue text.