Improve error message for locals index being out of bound

[plafer]

Currently, the following

proc.my_fn.3
  loc_loadw.0
end

(correctly) fails with the following error message

Failed to compile test source.:   x parameter value must be greater than or equal to 0 and less than or equal to 3, but was 4

We should improve the message by

1. including the source mapping to point to the offending line in the code, and
2. We should say "less than or equal to 0" rather than 3

• 3 is technically correct since loc_loadw indices are forced to be multiples of 4. But it would be more user-friendly if the error also rounded down 3 to 0