Sort includes when generating multiple files

[ruricolist]

Currently, when generating multiple files, it is possible for Datalog changes to result in spurious changes to otherwise unchanged generated files due to headers being reordered. This PR ensures that headers are always emitted in alphabetical order.

In my tests this reduces the number of files that need to be recompiled after a Datalog change by 15-20%.

[b-scholz]

Thanks for the improvement!

[codecov]

Codecov Report

Merging #2363 (1dd3cc8) into master (3047414) will increase coverage by 0.06%.
The diff coverage is 87.50%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2363      +/-   ##
==========================================
+ Coverage   77.43%   77.49%   +0.06%     
==========================================
  Files         470      467       -3     
  Lines       29332    30684    +1352     
==========================================
+ Hits        22713    23779    +1066     
- Misses       6619     6905     +286     

Impacted Files	Coverage Δ
src/synthesiser/GenDb.h	93.75% <78.26%> (-1.34%)	⬇️
src/main.cpp	69.49% <100.00%> (+0.27%)	⬆️
src/synthesiser/GenDb.cpp	97.15% <100.00%> (+1.09%)	⬆️
src/synthesiser/Synthesiser.cpp	84.78% <100.00%> (-0.13%)	⬇️
src/ast/utility/Utils.h	85.71% <0.00%> (-14.29%)	⬇️
src/ram/utility/NodeMapper.cpp	88.88% <0.00%> (-11.12%)	⬇️
src/ram/TranslationUnit.cpp	33.33% <0.00%> (-6.67%)	⬇️
src/ast/transform/Meta.cpp	60.00% <0.00%> (-6.67%)	⬇️
src/ast/analysis/SCCGraph.h	93.75% <0.00%> (-6.25%)	⬇️
src/ast/QualifiedName.h	94.11% <0.00%> (-5.89%)	⬇️
... and 194 more