[clang-tools-extra] [clang-tidy] Adds readability-redundant-const check (PR #189733)

[Berkay Sahin via cfe-commits]

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@@ -0,0 +1,94 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "RedundantConstCheck.h"
+#include "../utils/LexerUtils.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include <optional>
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::readability {
+
+static std::optional<Token>
+findConstToRemove(const VarDecl *VD, const MatchFinder::MatchResult &Result) {
+  const SourceManager &SM = *Result.SourceManager;
+
+  const SourceLocation NameBeginLoc = VD->getQualifier()
+                                          ? VD->getQualifierLoc().getBeginLoc()
+                                          : VD->getLocation();
+
+  const bool IsPointer = VD->getType()->isPointerType() ||
+                         VD->getType()->isNullPtrType() ||
+                         VD->getType()->isMemberPointerType();
----------------
berkaysahiin wrote:

When that is removed this:

```cpp
constexpr const decltype(nullptr) n = nullptr;

```
follows the non-pointer path and gives a warning on `const` as redundant. Do we want to warn on this ?

https://github.com/llvm/llvm-project/pull/189733