GODRIVER-2702 Update bsoncore value string to preserve timestamp type

[prestonvasquez]

GODRIVER-2702

Summary

Update the "bsoncore.Value#String" method to preserve timestamp int/uint type during string conversion. This method is intended to express BSON as extended JSON and converting the timestamp (I,U) values is in antithesis to specifications.

Background & Motivation

The "CommandStartedMessage" for command logging and monitoring has a field called "command" which is the "relaxed extJSON representation of the command." To accomplish this in the Go Driver, we use the "bsoncore.Value#String" method to convert cmdCopy in the operation executor to a string before logging. However, "bsoncore.Value#String" does not preserve timestamp types and so decoding the resulting string will result in the following error:

var doc bson.Raw
if err := bson.UnmarshalExtJSON([]byte(cmdCopy.String()), true, &doc); err != nil {
        // panic: error: $timestamp t value should be uint32, but instead is string
	panic(fmt.Sprintf("error: %v", err)) 
}

This use-case arises with the addition of the "$$matchAsDocument" and "$$matchAsRoot" operators to the driver test runners, here.

[matthewdale]

Looks good 👍

[benjirewis]

For clarity, what was the result of this before the change to value.go?

[prestonvasquez]

value_test.go:673: return values at index 0 are not equal. got {"$timestamp":{"t":"12345","i":"67890"}}; want {"$timestamp":{"t":12345,"i":67890}}