chore: use optional chaining

[trivikr]

Issue #, if available:
Refs: #1015

Description of changes:
Support for Optional Chaining was added in TS 3.7
https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html#optional-chaining

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov-io]

Codecov Report

Merging #1021 into smithy-codegen will not change coverage.
The diff coverage is 100%.

@@               Coverage Diff               @@
##           smithy-codegen    #1021   +/-   ##
===============================================
  Coverage           91.36%   91.36%           
===============================================
  Files                 144      144           
  Lines                2837     2837           
  Branches              502      504    +2     
===============================================
  Hits                 2592     2592           
  Misses                245      245

Impacted Files	Coverage Δ
packages/body-checksum-node/src/index.ts	100% <100%> (ø)	⬆️
...kages/fetch-http-handler/src/fetch-http-handler.ts	95.45% <100%> (ø)	⬆️
packages/property-provider/src/chain.ts	100% <100%> (ø)	⬆️
packages/middleware-stack/src/MiddlewareStack.ts	88.61% <100%> (ø)	⬆️
...ackages/node-http-handler/src/node-http-handler.ts	100% <100%> (ø)	⬆️
packages/middleware-retry/src/retryDecider.ts	100% <100%> (ø)	⬆️
packages/chunked-stream-reader-node/src/index.ts	100% <100%> (ø)	⬆️
packages/body-checksum-browser/src/index.ts	100% <100%> (ø)	⬆️
packages/signature-v4/src/getCanonicalHeaders.ts	100% <100%> (ø)	⬆️
...ckages/node-http-handler/src/node-http2-handler.ts	81.35% <100%> (ø)	⬆️
... and 1 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update a447740...e5ea4a5. Read the comment docs.

[aws-sdk-js-automation]

AWS CodeBuild CI Report

• CodeBuild project: sdk-staging-test
• Commit ID: e5ea4a5
• Result: SUCCEEDED
• Build Logs (available for 30 days)

Powered by github-codebuild-logs, available on the AWS Serverless Application Repository

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs and link to relevant comments in this thread.