[clang-tools-extra] [clang-tidy] Add performance-redundant-lookup check (PR #125420)

[Kazu Hirata via cfe-commits]

kazutakahirata wrote:

@steakhal, I don't meant to delay the landing of this PR, but I just want to bring up the following.  I'm wondering if your checker can catch repeated lookups within a loop like so:

```
for (int A : Vec)
  Map[Key].push_back(A);
```

in a function that does not reference `Map` anywhere else.  That is, statically, there is only one statement doing map lookups, but dynamically, the same lookup is repeated over and over.  Thanks!


https://github.com/llvm/llvm-project/pull/125420