[clang] [NFC][Static Analyzer] Rename and discuss about `NotNullConstraint` & `NotNullBufferConstraint` (PR #131374)

[Ziqing Luo via cfe-commits]

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@@ -436,9 +436,9 @@ class StdLibraryFunctionsChecker
                                llvm::raw_ostream &Out) const override;
 
     ValueConstraintPtr negate() const override {
-      NotNullBufferConstraint Tmp(*this);
+      BufferNullnessConstraint Tmp(*this);
       Tmp.CannotBeNull = !this->CannotBeNull;
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ziqingluo-90 wrote:

Oh, I somehow thought the checker passes a pre-condition `C` only when `State->assume(C) && !State->assume(!C))` but the reality is it reports a violation only when `State->assume(!C) && !State->assume(C)`.

Yes, you are right. This is fine.   

https://github.com/llvm/llvm-project/pull/131374