Add Happy Eyeballs support to TCPConnector

[illia-v]

What do these changes do?

They add Happy Eyeballs support to TCPConnector and enable it by default.

Are there changes in behavior for the user?

aiohttp should become more responsive to users having dual-stack configuration.

For example, Go enabled Happy Eyeballs (Fast Fallback) by default in 2018 golang/go@efc1850.

Also, in #4446 (comment) @asvetlov wrote that Happy Eyeballs may help with enabling aiodns by default. But I would not do so for now because pycares that is a dependency of aiodns uses an old version of c-ares that has security vulnerabilities.

Related issue number

Closes #4451

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
  • The format is <Name> <Surname>.
  • Please keep alphabetical order, the file is sorted by names.
• Add a new news fragment into the CHANGES folder
  • name it <issue_id>.<type> for example (588.bugfix)
  • if you don't have an issue_id change it to the pr id after creating the pr
  • ensure type is one of the following:
    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
    • .removal: Signifying a deprecation or removal of public API.
    • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example: "Fix issue with non-ascii contents in doctest text files."

[codecov]

Codecov Report

Merging #5471 (44e4a76) into master (10c8ce9) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #5471   +/-   ##
=======================================
  Coverage   97.17%   97.17%           
=======================================
  Files          41       41           
  Lines        8769     8774    +5     
  Branches     1404     1405    +1     
=======================================
+ Hits         8521     8526    +5     
  Misses        130      130           
  Partials      118      118           

Flag	Coverage Δ
unit	97.04% <83.33%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
aiohttp/connector.py	96.54% <100.00%> (+0.02%)	⬆️

---

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 10c8ce9...44e4a76. Read the comment docs.

[webknjaz]

Adding runtime-dependent behavior defaults is not the best idea: it should be consistent across envs. I don't think we should enable this by default but rather make it opt-in for as long as we support CPython versions below 3.8. If we were to have it on by default, it needs to be supported across all runtimes equally, otherwise, end-users would be confused as to what magic happens in some envs but not others, for example, by relying on a backport.

Also, this sort of change needs to be bundled with updates to tests and to docs.

[illia-v]

I am closing this because the change has no effect 🙁. See #4451 (comment)