Correctly support endpoint expressions with multiple chained assigns

[alextwoods]

Correctly support endpoint expressions with multiple chained assigns.

Motivation and Context

Codegen for endpoint rules with expressions with multiple chained assigns were failing because we our codegen would visit each assign and collect them and then after all were visited only then generate the lets, but since the generating the lets is what updates the symbol table we were not able to find the result of earlier assigns. Basically an endpoint rule like:

isoArn = aws.parseArn(ResourceARN) && isoArnType = isoArn.resourceId[0] 

In the above expression the isoArnType assign needs to use the resul tof the first assing to isoArn, which currently fails with:

  Cannot find a member with name `resourceId` for type `Void`,  
  Cannot find type for expression `(get-member isoArn resourceId)`,  
  Cannot find type for variable `isoArnType`,

Modifications

When visiting letExpressions we need to visit and process them sequentially - that is, we need to process the bindings AND register the types.

Testing

Added codegen test with previously failing example ruleset.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Checklist

• I have read the CONTRIBUTING document
• Local run of mvn install succeeds
• My code follows the code style of this project
• I have added tests to cover my changes
• All new and existing tests passed
• I have added a changelog entry. Adding a new entry must be accomplished by running the scripts/new-change script and following the instructions. Commit the new file created by the script in .changes/next-release with your changes.

License

• I confirm that this pull request can be released under the Apache 2 license

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