Added `try_exists()` method to `std::path::Path`

Added `try_exists()` method to `std::path::Path`

This method is similar to the existing `exists()` method, except it
doesn't silently ignore the errors, leading to less error-prone code.

This change intentionally does NOT touch the documentation of `exists()`
nor recommend people to use this method while it's unstable.
Such changes are reserved for stabilization to prevent confusing people.

Apart from that it avoids conflicts with #80979.