LSC: Replace uses of `int64` with `int64_t` and similar integer type aliases.

This LSC is part of an effort described in go/totw/190 to delete
third_party/absl/base/integral_types.h, and improve consistency between google3
and the external C++ community.

This change also replaces uses of other symbols defined in
third_party/absl/base/integral_types.h. For instance, `kint64max` will be
replaced with `std::numeric_limits<int64_t>::max()`.

For documentation regarding this LSC, see go/remove-integral-types-lsc.
For historical background, see go/remove-integral-types.

Tested:
    Some test failures are present, but the CL author has decided to mail the change anyway
PiperOrigin-RevId: 379611688