Add support for array slice

While working on https://github.com/apache/arrow-datafusion/pull/8946, I discovered that sqlparser-rs does not support tokens such as `[-1:-1]` or `[-2:3]`.

No files or tests are named in the issue. Start by reproducing the parser behavior for `[-1:-1]` and `[-2:3]`, then trace where array-slice syntax is parsed and add coverage for the reported forms. Done means the parser accepts these slice expressions without errors.

Written by the indexing model from the issue text.