♻ Change a dict() for {} in fastapi/utils.py

[ShahriyarR]

In general dict() call is considered slower than direct {}.
The internal representations are also different, there is no extra function call while constructing the map with {}

>>> import dis
>>> dis.dis('{}')
  1           0 BUILD_MAP                0
              2 RETURN_VALUE
>>> dis.dis('dict()')
  1           0 LOAD_NAME                0 (dict)
              2 CALL_FUNCTION            0
              4 RETURN_VALUE

There are bunch of similar cases in FastAPI source code, I will send PRs accordingly.

[codecov]

Codecov Report

Merging #3138 (3a91387) into master (ce0ec06) will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff             @@
##            master     #3138     +/-   ##
===========================================
  Coverage   100.00%   100.00%             
===========================================
  Files          243       531    +288     
  Lines         7419     13629   +6210     
===========================================
+ Hits          7419     13629   +6210     

Impacted Files	Coverage Δ
fastapi/utils.py	100.00% <ø> (ø)
fastapi/params.py	100.00% <0.00%> (ø)
fastapi/routing.py	100.00% <0.00%> (ø)
fastapi/encoders.py	100.00% <0.00%> (ø)
fastapi/responses.py	100.00% <0.00%> (ø)
fastapi/exceptions.py	100.00% <0.00%> (ø)
fastapi/concurrency.py	100.00% <0.00%> (ø)
fastapi/applications.py	100.00% <0.00%> (ø)
fastapi/openapi/docs.py	100.00% <0.00%> (ø)
tests/test_ws_router.py	100.00% <0.00%> (ø)
... and 318 more

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[github-actions]

📝 Docs preview for commit 8f737f7 at: https://608d2773115ff8084ddb1b76--fastapi.netlify.app

[cikay]

The commit message should be "Replace empty dict literal with built-in dict function"

You can also specifiy the reason in the body of the commit which should be performance optimization

[github-actions]

📝 Docs preview for commit 3a91387 at: https://627e32546e589151aede165c--fastapi.netlify.app

[tiangolo]

Thanks @ShahriyarR! 🚀

Also, don't worry about the commit messages, I update the PR title and squash and merge afterwards, so I take care of keeping the commits consistent with the style of the code.