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

[Berkay Sahin via cfe-commits]

================
@@ -0,0 +1,171 @@
+// RUN: %check_clang_tidy -std=c++11-or-later %s readability-redundant-const %t
+
+struct Foo {};
+
+constexpr int n1 = 10;
+const int n2 = 20;
+constexpr Foo n3 = {};
+
+constexpr const int p1 = 10;
----------------
berkaysahiin wrote:

```cpp
constexpr const int const p2 = 0
```

What do we expect here ? Clang already warns about the second const as redundant. This check can only remove of the const's atm, so it becomes

```cpp
constexpr const int p2 = 0
```

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