Add subsection explaining the Block Deduplicator step of the Optimizer

## Page

Opcode-based Optimizer Section of the documentation.

https://docs.soliditylang.org/en/v0.8.23/internals/optimizer.html#opcode-based-optimizer-module

## Abstract

Requested here: https://github.com/ethereum/solidity-website/pull/57#discussion_r1384926540
The block deduplicator is not covered by the documentation and a subsection explaining it is needed.

Start with the linked Opcode-based Optimizer section in the Solidity documentation, especially the referenced optimizer page and its block deduplicator step. Add a subsection explaining the block deduplicator, and consider the work complete when that optimizer step is documented in the appropriate section.

Written by the indexing model from the issue text.