[clang-tidy] Add support for determining constness of more expressions. (#82617)
This uses a more systematic approach for determining whcich
`DeclRefExpr`s mutate the underlying object: Instead of using a few
matchers, we walk up the AST until we find a parent that we can prove
cannot change the underlying object.
This allows us to handle most address taking and dereference, bindings
to value and const& variables, and track constness of pointee (see
changes in DeclRefExprUtilsTest.cpp).
This allows supporting more patterns in
`performance-unnecessary-copy-initialization`.
Those two patterns are relatively common:
```
const auto e = (*vector_ptr)[i]
```
and
```
const auto e = vector_ptr->at(i);
```
In our codebase, we have around 25% additional findings from
`performance-unnecessary-copy-initialization` with this change. I did
not see any additional false positives.
GitOrigin-RevId: 94ca854d3c874322b1d4b5606c5762adcd3b8e05
6 files changed
