Re-use bindings when values are identical

[tantaman]

If I have the query:

sql`SELECT * FROM foo WHERE a = ${some_big_value} OR b = ${some_big_value}`

it should ideally generate:

{
  text: `SELECT * FROM foo WHERE a = $1 OR b = $1,
  values: [some_big_value]
}

rather than

{
  text: `SELECT * FROM foo WHERE a = $1 OR b = $2,
  values: [some_big_value, some_big_value]
}

I've implemented this via my own formatFunction here: rocicorp/mono#4112

but seems like this should be an option in the library.