[clang] Replace None with std::nullopt in comments (NFC)

This is part of an effort to migrate from llvm::Optional to
std::optional:

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716

clang/include/clang/AST/ExprCXX.h

@@ -2321,7 +2321,7 @@ class CXXNewExpr final
 
   /// This might return std::nullopt even if isArray() returns true,
   /// since there might not be an array size expression.
-  /// If the result is not-None, it will never wrap a nullptr.
+  /// If the result is not std::nullopt, it will never wrap a nullptr.
   std::optional<Expr *> getArraySize() {
     if (!isArray())
       return std::nullopt;
@@ -2335,7 +2335,7 @@ class CXXNewExpr final
 
   /// This might return std::nullopt even if isArray() returns true,
   /// since there might not be an array size expression.
-  /// If the result is not-None, it will never wrap a nullptr.
+  /// If the result is not std::nullopt, it will never wrap a nullptr.
   std::optional<const Expr *> getArraySize() const {
     if (!isArray())
       return std::nullopt;

clang/include/clang/Basic/DiagnosticError.h

@@ -35,8 +35,8 @@ class DiagnosticError : public llvm::ErrorInfo<DiagnosticError> {
   }
 
   /// Extracts and returns the diagnostic payload from the given \c Error if
-  /// the error is a \c DiagnosticError. Returns none if the given error is not
-  /// a \c DiagnosticError.
+  /// the error is a \c DiagnosticError. Returns std::nullopt if the given error
+  /// is not a \c DiagnosticError.
   static std::optional<PartialDiagnosticAt> take(llvm::Error &Err) {
     std::optional<PartialDiagnosticAt> Result;
     Err = llvm::handleErrors(std::move(Err), [&](DiagnosticError &E) {

clang/include/clang/ExtractAPI/Serialization/SymbolGraphSerializer.h

@@ -67,7 +67,7 @@ class SymbolGraphSerializer : public APISerializer {
   ///
   /// \returns an optional JSON Object representing the payload that libclang
   /// expects for providing symbol information for a single symbol. If this is
-  /// not a known symbol returns \c None.
+  /// not a known symbol returns \c std::nullopt.
   static std::optional<Object> serializeSingleSymbolSGF(StringRef USR,
                                                         const APISet &API);
 

clang/include/clang/Lex/Lexer.h

@@ -551,7 +551,7 @@ class Lexer : public PreprocessorLexer {
 
   /// Finds the token that comes right after the given location.
   ///
-  /// Returns the next token, or none if the location is inside a macro.
+  /// Returns the next token, or std::nullopt if the location is inside a macro.
   static std::optional<Token> findNextToken(SourceLocation Loc,
                                             const SourceManager &SM,
                                             const LangOptions &LangOpts);

clang/lib/Analysis/UnsafeBufferUsage.cpp

@@ -332,7 +332,7 @@ class FixableGadget : public Gadget {
   bool isWarningGadget() const final { return false; }
 
   /// Returns a fixit that would fix the current gadget according to
-  /// the current strategy. Returns None if the fix cannot be produced;
+  /// the current strategy. Returns std::nullopt if the fix cannot be produced;
   /// returns an empty list if no fixes are necessary.
   virtual std::optional<FixItList> getFixits(const Strategy &) const {
     return std::nullopt;

clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp

@@ -1083,7 +1083,7 @@ areFeasible(ConstraintRangeTy Constraints) {
 ///
 /// \returns true if assuming this Sym to be true means equality of operands
 ///          false if it means disequality of operands
-///          None otherwise
+///          std::nullopt otherwise
 std::optional<bool> meansEquality(const SymSymExpr *Sym) {
   switch (Sym->getOpcode()) {
   case BO_Sub:

clang/unittests/Analysis/FlowSensitive/MultiVarConstantPropagationTest.cpp

@@ -57,7 +57,8 @@ struct ValueLattice {
   //  * `Defined` -> top.
   ValueState State;
 
-  // When `None`, the lattice is either at top or bottom, based on `State`.
+  // When `std::nullopt`, the lattice is either at top or bottom, based on
+  // `State`.
   std::optional<int64_t> Value;
 
   constexpr ValueLattice()

clang/unittests/Analysis/FlowSensitive/SingleVarConstantPropagationTest.cpp

@@ -59,7 +59,7 @@ struct ConstantPropagationLattice {
       return Lhs.Var == Rhs.Var && Lhs.Value == Rhs.Value;
     }
   };
-  // `None` is "bottom".
+  // `std::nullopt` is "bottom".
   std::optional<VarValue> Data;
 
   static constexpr ConstantPropagationLattice bottom() {