Add RAII (CloseApi) annotation for PIDL types (ITEMIDLIST) so CsWin32 generates an ILFree SafeHandle

[antmor]

Problem

PIDLs (PIDLIST_ABSOLUTE, PIDLIST_RELATIVE, PITEMID_CHILD -> ITEMIDLIST*) are heap allocations that must be released with ILFree (CoTaskMemFree). Today they are projected as plain pointers with no RAII, so CsWin32 consumers must hand-roll a SafeHandle/try-finally around every SHGetIDListFromObject, ILCreateFromPath, SHGetKnownFolderIDList, etc. This is error-prone and inconsistent with how other free-based types are modeled.

Precedent / pattern

generation/WinSDK/autoTypes.json already models pointer-typedefs-with-a-free-function. The closest precedent is BSTR:

{ "Name": "BSTR", "ValueType": "char*", "CloseApi": "SysFreeString", "NativeTypedef": true }

CloseApi -> CsWin32 emits [RAIIFree(...)] -> generates a SafeHandle (per docs/projections.md, NativeTypedefStructsCreator.cs). Other free-based entries: HLOCAL->LocalFree, HMODULE->FreeLibrary, HDDEDATA->DdeFreeDataHandle.

Proposed change

Add PIDL typedefs to autoTypes.json with CloseApi: "ILFree/cotaskmemfree", generating e.g. ILFreeSafeHandle.

Design questions for maintainers

1. ILFree takes PIDLIST_RELATIVE; should all three PIDL typedefs share one SafeHandle via AlsoUsableFor (as HMODULE/HINSTANCE do)?
2. These are [wire_marshal] typedefs (typedef ITEMIDLIST_ABSOLUTE* PIDLIST_ABSOLUTE) - does the scraper model them cleanly as NativeTypedef?
3. Interaction with More issues with SHGetFileInfo #2160 (the SHGetFileInfo all-or-nothing friendly-overload problem) when a PIDL out-param becomes a SafeHandle return.

Related: #2160