Double values should always be serialized with decimal point

[russcam]

With the move to utf8json in #3493, floating point and decimal numbers that do not have fractional values are not serialized with decimal point by utf8json. This saves a few bytes, but would break Elasticsearch type mapping inference. Floating point and decimals should always be sent with a decimal point.

[russcam]

Closing this as #3660 has been merged into 7.x