Fix ValidateCounterId so an ID exactly equal to MaxCounterId also fails

[strangelydim]

NOTE: This PR being created as a draft for discussion.

Java's maxCounterId is set to:

this.maxCounterId = (valuesBuffer.capacity() / COUNTER_LENGTH) - 1;

whereas .NET's is:

MaxCounterId = valuesBuffer.Capacity / COUNTER_LENGTH;

The better fix, IMO, is to change .NET to match Java, so "max counter ID" really is the max counter ID, not one higher than the max ID.

However, it's a public value, and users might already have code that uses it, so that would be a potentially breaking change.

The change in this PR is the simpler, non-breaking thing we could do. Which do we prefer?