types: support non-SQL styles of ds.execute

[bajtos]

Add new overloads for DataSource.execute method to support non-SQL connectors like MongoDB.

See loopbackio/loopback-next#3342 for background and https://loopback.io/doc/en/lb3/Executing-native-SQL.html for the existing documentation for db.execute API.

Checklist

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• npm test passes on your machine
• New tests added or existing tests modified to cover all changes
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[jannyHou]

LGTM in general 👍 a minor comment.

[jannyHou]

nitpick: the execute function in mongodb seems doesn't have a 3rd parameter, see
https://github.com/strongloop/loopback-connector-mongodb/blob/master/lib/mongodb.js#L467

[bajtos]

I appreciate your attention to details! 👍

MongoDB connector's execute function does not describe additional parameters in the function signature, but uses arguments.slice to access them:

https://github.com/strongloop/loopback-connector-mongodb/blob/c58e9fbe2b4161230751baf0385cb4c4f6958519/lib/mongodb.js#L469-L470

  // Get the parameters for the given command
  const args = [].slice.call(arguments, 2);

This code was written before rest parameters were introduced to the language, therefore it was not possible to encode ...parameters in the function signature.