[clang] [llvm] [clang] Add/enhance documentation for some important classes. (PR #109795)

[Alexandre Ganea via cfe-commits]

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@@ -7,7 +7,10 @@
 //===----------------------------------------------------------------------===//
 //
 /// \file
-/// Defines the virtual file system interface vfs::FileSystem.
+/// Provides abstract filesystem APIs to decouple from OS-level file access.
+///
+/// This allows replacing access to physical files on disk by in-memory data,
+/// for testing or other purposes.
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aganea wrote:

for testing, **caching** or other purposes.

https://github.com/llvm/llvm-project/pull/109795