Adjust `explicit-function-return-type` settings

[mrmckeb]

We've enabled @typescript-eslint/explicit-function-return-type in our latest canary release, but we should probably.

• allowExpressions - I feel this should be on as it'll reduce pain, with minimal risk.
• allowTypedFunctionExpressions - I feel this should be on as it'll reduce pain.
• allowHigherOrderFunctions - I feel this should stay off.
• allowDirectConstAssertionInArrowFunctions - I'm not sure about this, but I'd lean towards off too... as a type would be better.
• allowConciseArrowFunctionExpressionsStartingWithVoid - I feel we can keep this off.

See: https://typescript-eslint.io/rules/explicit-function-return-type/

[mrmckeb]

After assessing this we've decided to stick with the default settings for now.