Fixes to isFunctionCallExternal() after end-to-end test

[blitz-1306]

Preface

Test of pending release against Scribble uncovered additional edge-cases for external call detection:

• We sometimes may have ContractType.method() member accesses for public functions, where ContractType is one of the inheritance bases. Some of those calls are invoked internally. Example is here.
• FunctionLikeSetTypes are now yet handled, where we have various possible functions via overloading. Example is here.

This PR makes attempts to address these issues. Related Scribble tuning PR is here: Consensys/scribble#232

Changes

• Reintroduce isFunctionCallExternal() as method of InferType.
• Improved detection of calls in external context.
• Added relevant cases to a test sample.

Notes

This is a breaking change (previous PR #213 was also breaking due to signature change), so pending release would have to bump major version of the package to avoid breaking dependencies.

Regards.

[codecov-commenter]

Codecov Report

Merging #215 (4ea38d2) into master (18444a4) will increase coverage by 0.08%.
The diff coverage is 92.30%.

@@            Coverage Diff             @@
##           master     #215      +/-   ##
==========================================
+ Coverage   91.65%   91.73%   +0.08%     
==========================================
  Files         267      267              
  Lines        6527     6549      +22     
  Branches     1307     1320      +13     
==========================================
+ Hits         5982     6008      +26     
+ Misses        289      287       -2     
+ Partials      256      254       -2     

Impacted Files	Coverage Δ
src/types/infer.ts	82.59% <92.10%> (+0.59%)	⬆️
src/types/utils.ts	88.10% <100.00%> (+0.10%)	⬆️

... and 2 files with indirect coverage changes

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[cd1m0]

One question, some nits. Otherwise looking decent!