Fix for dependency loop issue

[intel352]

what

• Refactored to better identify and track dependencies
• This solved issue local.lookup_transit_gateway : The "count" value depends on resource attributes that cannot be determined until apply #51 for me, which preventing terraform planning.

why

• The previous logic had references to potentially non-existent objects peppered throughout the code, and didn't have a proper dependency chain identified
• As a result, resource attributes couldn't be calculated until apply

references

Fixes #51