feat: add default_return_value kwarg for calls

[charles-cooper]

What I did

implement #2812

How I did it

How to verify it

Commit message

this commit adds a new kwarg, `default_return_value`, available to all
external calls. its purpose is to make it easier to interface with
contracts which are not compliant with their interfaces (e.g., bad ERC20
implementations) without having to drop down to `raw_call`.

since the logic for handling kwargs in `external_call.py` was getting a
little gnarly, this commit also refactors and that module a bit. for
consistency, it also switches to exclusively using the
typechecker type of the function.

Commit message for the final, squashed PR. (Optional, but reviewers will appreciate it! Please see our commit message style guide for what we would ideally like to see in a commit message.)

Description for the changelog

add default_return_value kwarg for external calls.

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[codecov-commenter]

Codecov Report

Merging #2839 (fa21400) into master (efe1dbe) will increase coverage by 0.02%.
The diff coverage is 96.29%.

❗ Current head fa21400 differs from pull request most recent head 83f030b. Consider uploading reports for the commit 83f030b to get more accurate results

@@            Coverage Diff             @@
##           master    #2839      +/-   ##
==========================================
+ Coverage   87.65%   87.67%   +0.02%     
==========================================
  Files          94       94              
  Lines       10179    10183       +4     
  Branches     2503     2501       -2     
==========================================
+ Hits         8922     8928       +6     
+ Misses        791      790       -1     
+ Partials      466      465       -1     

Impacted Files	Coverage Δ
vyper/codegen/expr.py	80.73% <ø> (ø)
vyper/semantics/types/function.py	87.21% <80.00%> (+0.09%)	⬆️
vyper/codegen/external_call.py	98.07% <97.36%> (+1.99%)	⬆️

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[lgtm-com]

This pull request introduces 1 alert when merging ced9e66 into efe1dbe - view on LGTM.com

new alerts:

• 1 for Syntax error