better handling of unknown components in .init

[quentin]

• Detect unknown component at .init instead of post-flattening late detection of missing elements.
• Update the negative test.
• Add a positive test demonstrating complex chain of component argument passing.

[codecov]

Codecov Report

Merging #2450 (8d58eab) into master (2914f7b) will increase coverage by 0.18%.
Report is 26 commits behind head on master.
The diff coverage is 78.01%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2450      +/-   ##
==========================================
+ Coverage   77.75%   77.94%   +0.18%     
==========================================
  Files         474      482       +8     
  Lines       31164    31948     +784     
==========================================
+ Hits        24232    24901     +669     
- Misses       6932     7047     +115     

Files	Coverage Δ
src/FunctorOps.cpp	60.81% <ø> (ø)
src/RelationTag.h	53.03% <ø> (+0.79%)	⬆️
src/ast/Aggregator.cpp	95.65% <100.00%> (+0.19%)	⬆️
src/ast/Aggregator.h	100.00% <ø> (ø)
src/ast/Attribute.h	100.00% <100.00%> (ø)
src/ast/Component.h	100.00% <ø> (ø)
src/ast/IterationCounter.cpp	100.00% <100.00%> (ø)
src/ast/Lattice.h	100.00% <100.00%> (ø)
src/ast/Program.h	100.00% <ø> (ø)
src/ast/QualifiedName.h	94.11% <ø> (ø)
... and 82 more

... and 6 files with indirect coverage changes