HPCC-12036 Warn if floating point indices used when perhaps a range was ...

...intended

I'm not %100 on the actual warning message.
Also, I wondered if I should consolidate into a single routine, either as a static within hqlgram.y or as a method of HqlGram. didn't choose the later as couldn't come up with a suitable name due to how specific it should be and lack of reuse. Nor the first as I believe we wish to avoid these.

Signed-off-by: jamienoss <james.noss@lexisnexis.com>
NOTE: This line will cause a seg fault if -wmistake!=error until https://track.hpccsystems.com/browse/HPCC-12285 is resolved.