The current semantic check in place is incorrect, this patch fixes this.
Up to 1 **'default'** named mapper should be allowed for each derived
type.
The current semantic check only allows up to 1 **'default'** named
mapper across all derived types.
This also makes sure that declare mappers follow proper scoping rules
for both default and named mappers.
Co-authored-by: Raghu Maddhipatla <Raghu.Maddhipatla@amd.com>
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