R320-018 fix external default in imported project

Refactor For_Each_External_Variable_Declaration,
get rig of useless nested procedure, put better names
for arguments and variables.
Pass proper parameters to variable registration routines,
remove excess ones that can be calculated from passed
project type.
Use proper project when calculating the expression
value instead of the root one.
Detect and pass proper package to expression calculation.
Pass project node instead of variable node as
From_Project_Node to Expression.
Add test.

Change-Id: I1abe615368ce284984155f820023c1c86807f6d5