[clang-tidy] Add `modernize-use-as-const` check

It would be useful to have a clang-tidy check that recognizes common ways of treating an lvalue as `const` and suggests `std::as_const` in C++17 and later.

Today code like this is fairly common:

```cpp
use(static_cast(obj));

for (const auto &x : static_cast(c)) {
...
}
```

but the clearer modern spelling is:

```cpp
use(std::as_const(obj));

for (const auto &x : std::as_const(c)) {
...
}
```

This makes the intent explicit: the code is not performing an arbitrary cast, it is simply viewing an existing object as const.