Fixed Lambda handler for compiled languages

[leo]

Interpreted languages deployed to AWS Lambda use the following format for the handler of a Lambda:

<file-name-without-extension>.<method-name>

Compiled languages, on the other hand, use this format:

<file-name>

The latter previously wasn't supported at all, but after this change, it will be.

The logic does not rely on actually knowing whether a compiled or interpreted language is used. Instead, it just checks if the handler exists as-is on the file system, and if it does, it's considered a compiled language. If that's not the case, the first format is assumed and used instead.

After this change, the error shown on the "Errors" tab of this Deployment should disappear.

It works with vercel-plugin-go, vercel-plugin-ruby, and vercel-plugin-python.

Tests

• The code changed/added as part of this PR has been covered with tests
• All tests pass locally with yarn test-unit

Code Review

• This PR has a concise title and thorough description useful to a reviewer
• Issue from task tracker has a link to this PR

[codecov]

Codecov Report

Merging #7129 (28ed23f) into main (5f5e50c) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #7129   +/-   ##
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  Coverage   51.49%   51.49%           
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  Files         128      128           
  Lines        4979     4979           
  Branches     1212     1212           
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  Hits         2564     2564           
  Misses       2403     2403           
  Partials       12       12           

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[styfle]

Looks good but it should add a new test, perhaps for Go, to prove it works correctly

[leo]

Sounds great — I'll add some tests for all three shortly, once they work in production.