[clang] [libclang] Document CXUnsavedFile::Length width and fix test narrowing (PR #228405)

[via cfe-commits]

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@@ -118,6 +118,9 @@ struct CXUnsavedFile {
 
   /**
    * The length of the unsaved contents of this buffer.
+   *
+   * Note that this is an \c unsigned \c long, which has a platform-dependent
+   * width. Do not assume it is a 64-bit integer.
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UebelAndre wrote:

This part of the change ultimately came from diving into https://github.com/llvm/llvm-project/issues/160729 and wasn't entirely sure what the resolution should be especially since the issue was solved externally. If the comment feels too pedantic I think the discourse on the PR and some note in the commit message would probably be sufficient in communicating this? I'm happy to make whatever changes folks would like to see 😄 

https://github.com/llvm/llvm-project/pull/228405