chore(deps-dev): bump typescript to ~3.9.3

[trivikr]

Issue #, if available:
N/A

Description of changes:
bump typescript to ~3.9.3

new build (post git clean -dfx and yarn):

$ typescript ~3.8.3
Done in 381.79s.
yarn build:all  5200.27s user 191.69s system 1411% cpu 6:21.92 total

$ typescript ~3.9.3
Done in 347.24s.
yarn build:all  4770.80s user 183.97s system 1426% cpu 5:47.37 total

repeat build

$ typescript ~3.8.3
Done in 113.29s.
yarn build:all  1467.44s user 90.27s system 1373% cpu 1:53.42 total

$ typescript ~3.9.3
Done in 115.64s.
yarn build:all  1499.69s user 90.40s system 1373% cpu 1:55.77 total

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

[codecov-commenter]

Codecov Report

Merging #1347 into master will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1347      +/-   ##
==========================================
+ Coverage   77.67%   77.68%   +0.01%     
==========================================
  Files         286      287       +1     
  Lines       11955    11976      +21     
  Branches     2623     2631       +8     
==========================================
+ Hits         9286     9304      +18     
- Misses       2669     2672       +3     

Impacted Files	Coverage Δ
.../middleware-sdk-transcribe-streaming/src/signer.ts	80.00% <100.00%> (ø)
packages/url-parser-node/src/index.ts	100.00% <0.00%> (ø)
...s/middleware-bucket-endpoint/src/bucketHostname.ts	100.00% <0.00%> (ø)
...s/middleware-bucket-endpoint/src/configurations.ts	100.00% <0.00%> (ø)
...er-cognito-identity/src/fromCognitoIdentityPool.ts	100.00% <0.00%> (ø)
packages/middleware-stack/src/MiddlewareStack.ts	88.66% <0.00%> (+0.05%)	⬆️
packages/signature-v4/src/moveHeadersToQuery.ts	92.30% <0.00%> (+1.39%)	⬆️

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[alexforsyth]

LGTM

[AllanZhengYP]

Approved! Do you need to update the codegen?

[trivikr]

Do you need to update the codegen?

Yup, will update codegen with all deps updates in a separate PR.
We should ideally accompany codegen updates in deps updates PRs, but most deps updates are done by depenedabot. May be we should prioritize moving clients to a separate repo to simplify ownership.

[github-actions]

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