Fix async function and variable declartions

[soda0289]

Async functions mark all variables as constants since the flags are not being read correctly. This patch uses the builtin typescript utilities functions to determine the variable declaration type.

Some tests are broken and I will need to add tests for this new case. Just looking for feedback.

[jsf-clabot]

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3 out of 4 committers have signed the CLA.

✅ soda0289
✅ JamesHenry
✅ flying-sheep
❌ ESLint Jenkins

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[eslintbot]

Thanks for the pull request, @soda0289! I took a look to make sure it's ready for merging and found some changes are needed:

• The commit summary must be 72 characters or shorter. Please check out our guide for how to properly format your commit summary and update it on this pull request.

Can you please update the pull request to address these?

(More information can be found in our pull request guide.)

[eslintbot]

Thanks for the pull request, @soda0289! I took a look to make sure it's ready for merging and found some changes are needed:

• The commit summary must be 72 characters or shorter. Please check out our guide for how to properly format your commit summary and update it on this pull request.

Can you please update the pull request to address these?

(More information can be found in our pull request guide.)

[eslintbot]

Thanks for the pull request, @soda0289! I took a look to make sure it's ready for merging and found some changes are needed:

• The commit summary must be 72 characters or shorter. Please check out our guide for how to properly format your commit summary and update it on this pull request.

Can you please update the pull request to address these?

(More information can be found in our pull request guide.)

[soda0289]

Replaced with pull request #138