[clang] [Modules] Enrich diags for out of date module dependencies (PR #190203)

[Cyndy Ishida via cfe-commits]

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@@ -120,6 +121,18 @@ class InputFile {
   bool isNotFound() const { return Val.getInt() == NotFound; }
 };
 
+/// Describes a single change detected in a module file or input file.
+struct Change {
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cyndyishida wrote:

1. Yes
2. It's also here because it's related to `InputFileValidation` and ultimately a property of a `ModuleFile`

https://github.com/llvm/llvm-project/pull/190203