[clang] [C++20][Modules] Implement P1857R3 Modules Dependency Discovery (PR #107168)

[Corentin Jabot via cfe-commits]

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@@ -297,6 +297,11 @@ class Token {
   /// Return the ObjC keyword kind.
   tok::ObjCKeywordKind getObjCKeywordID() const;
 
+  /// Return true if we have an C++20 Modules contextual keyword(export, import
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cor3ntin wrote:

```suggestion
  /// Return true if we have a C++20 modules contextual keyword(export, import,
```

https://github.com/llvm/llvm-project/pull/107168