Merge token-exchange into main repo

[mvines]

token-exchange is too far away and hard to work with. Let's

• [x] Bring token-exchange/client-demo into a subdirectory in the main repo like bench-exchange/
• [x] Add support for running bench-exchange instead of bench-tps in the net/ scripts
• [x] Migrate any remaining issues from token-exchange over to the main repo then delete the old repo

[jackcmay]

sgtm

[jackcmay]

@mvines If we change the swapper to the same mechanism the block explorer uses will we again need a separate repo than Solana?

[mvines]

@mvines If we change the swapper to the same mechanism the block explorer uses will we again need a separate repo than Solana?

We're good. All the support for the block streamer socket is in the main repo. Blockexplorer provides a JS program that reads from the socket, which wouldn't be helpful for the swapper, so we'd need to write a Rust version of that program -- but that thing would nicely slide into sdk/

[jackcmay]

Cool

[mvines]

cc: #3826

[jackcmay]

cc: #3893