Convert partial level 6 files to typescript for contributing to `metamask-controller.js`

[DDDDDanica]

Convert dependency of files for metamask-controller.js (level 2) we want to target based on typescript migration dashboard.

Level 6

• app/scripts/lib/rpc-method-middleware/handlers/add-ethereum-chain.js
• app/scripts/lib/rpc-method-middleware/handlers/eth-accounts.js
• app/scripts/lib/rpc-method-middleware/handlers/get-provider-state.js
• app/scripts/lib/rpc-method-middleware/handlers/log-web3-shim-usage.js
• app/scripts/lib/rpc-method-middleware/handlers/request-accounts.js
• app/scripts/lib/rpc-method-middleware/handlers/send-metadata.js
• app/scripts/lib/rpc-method-middleware/handlers/switch-ethereum-chain.js
• app/scripts/lib/rpc-method-middleware/handlers/watch-asset.js