Fix the initialization order in the interpreter

[turbolent]

Description

Initialize declarations in the same order as they are initialized in the checker.

In addition, change global variables to be initialized lazily, so that potential forward references, through e.g. functions, work properly.

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• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[codecov-commenter]

Codecov Report

Merging #958 (6887659) into master (8e3c230) will increase coverage by 0.03%.
The diff coverage is 100.00%.

❗ Current head 6887659 differs from pull request most recent head 9547869. Consider uploading reports for the commit 9547869 to get more accurate results

@@            Coverage Diff             @@
##           master     #958      +/-   ##
==========================================
+ Coverage   75.36%   75.40%   +0.03%     
==========================================
  Files         268      268              
  Lines       32666    32690      +24     
==========================================
+ Hits        24618    24649      +31     
+ Misses       6915     6910       -5     
+ Partials     1133     1131       -2     

Flag	Coverage Δ
unittests	75.40% <100.00%> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
runtime/ast/program.go	72.41% <100.00%> (+0.48%)	⬆️
runtime/ast/programindices.go	100.00% <100.00%> (ø)
runtime/interpreter/interpreter.go	90.45% <100.00%> (+0.22%)	⬆️
runtime/interpreter/interpreter_statement.go	89.13% <100.00%> (+0.49%)	⬆️
runtime/runtime_storage.go	87.87% <0.00%> (+1.01%)	⬆️
runtime/interpreter/variable_activations.go	84.44% <0.00%> (+2.22%)	⬆️
runtime/interpreter/variable.go	100.00% <0.00%> (+20.00%)	⬆️

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[SupunS]

LGTM!